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Pure Confusion – Finding the “Right” Water for Your Aquarium

Water SamplingOne common question that we receive about setting up new aquariums is about the most basic ingredient to the aquarium, the water that goes into it. There are a lot of terms that can get confusing when someone is trying to determine how to fill their aquarium and from what source. The options can be staggering – tap water, bottled water, prefilters, and so on – and starting with the right foundation can make all the difference, from the smallest betta bowl to the largest reef system.

Tap Water

This is probably the easiest and most accessible water source in most areas. Whether you get your water from a municipal water sources or from a well, it doesn’t get much easier than going to the nearest sink to fill your bucket or tank. Its ease is definitely a benefit, but keep in mind that municipal water sources will usually contain chlorine or chloramine to kill bacteria and well water sources may contain phosphates or other organics. Tap water can be used, but should be treated or purified to remove these materials before it goes into your aquarium.

Reverse Osmosis (RO) and De-ionized (DI) Water

RO/DI Units are very popular among aquarists. Although Reverse Osmosis and De-ionization are different processes, they are often done in conjunction and in combination filtration systems. In these units, water is forced through a membrane (RO) and through resins (DI) that remove minerals and compounds leaving the water very pure. A unit can be installed to filter tap water and make it safe to use for aquariums, but does not, in itself, remove chlorine and chloramine compounds used in tap water purification. Most newer RO/DI units have carbon prefilters to remove chlorine and chloramine before it gets to the aquarium. While RO/DI filtration removes most of what an aquarists does not want in their water source, it can also remove some of what one does want so RO/DI water must be buffered and “remineralized” before being used. Reef aquarists are the most common RO/DI users and since they use salt mixes before using the RO/DI water, they usually do not have to be concerned since the salt mix itself makes the water suitable for usage again. Anyone using RO/DI in a freshwater system would need to remineralize their water using a buffer appropriate to their system.

Distilled Water

Distilled water is one of the purest water types available. It is created by heating water and collecting the pure water that evaporates as steam while leaving solid impurities behind. This is not usually used by home aquarists since it tends to be expensive and more inefficient when it comes to tank maintenance, but distilled water is available in most grocery stores. Most often, it is questioned as a possible water source for smaller tanks like bettas, goldfish and community tanks and by new aquarists looking for an easier and “safer” solution.

Not necessarily. Since it is very pure and has had even more minerals and compounds removed than other processes, it is extremely soft and has no buffering capacity or mineral composition. As with RO/DI water, these minerals are often replaced if the distilled water is mixed with salt mixes for reef systems but it would need to be buffered before it can be used for freshwater or for a small system like a betta bowl. Without being buffered, the water chemistry parameters like pH can fluctuate wildly. For these smaller tanks and bowls, distilled water can be costly, inconvenient and even unsafe.

Spring Water and Bottled Water Sources

Spring water on MackinacBottled water is popular for those with small tank and for betta enthusiasts. Since it is available in most grocery stores and can be more convenient than dechlorinating tap water, many turn to bottled sources and different brands of spring water for quick water changes. While most spring water is filtered and safe to use, every brand is different and meets different standards. Most bottled water is filtered by reverse osmosis, deionization or distillation similar to the sources already discussed, and many brands add minerals back into the water to improve taste and nutritional value. “Spring water”, by definition, comes from an underground source and its mineral composition is affected by that source so its mineral make-up can vary as a result as well. It is a good idea to test a new brand for pH, hardness, phosphates, nitrates and other base readings before use, especially in a sensitive reef system.

Although the water sources may vary, the requirements of the fish, plants and animals we keep generally does not. If you have questions about how to make your water appropriate for what you want to put into it, feel free to let us know!



Spring water on Mackinac image referenced from wikipedia and originally posted by DaemonDivinus
Water sampling image referenced from wikipedia and originally posted by Alloquep


  1. avatar

    Hi, I am trying to farm Red Cherry Shrimp and the water in my areas PH and Hardness are extremely high. I have tried several PH neutral products and with multiple doses the best I can get is 7.6 using my API test kit. My first attempt at keeping these shrimp in my planted tank was a total loss. It is approximately a 20 Gallon tank with two pieces of small driftwood two air powered 20 gallon sponge filters and a small 20g CO2 system. any advice

  2. avatar

    Hi Christopher, High hardness is very difficult to fight against. I would recommend switching your water source rather than try to fight that water into submission. Since the tank is fairly small, you can purchase spring water for your water changes or invest in an RO (reverse Osmosis) unit for a more readily-available water supply. RO Units are pretty popular for situations like yours when a home water softener isn’t a practical solution and they can be found from aquariums stores like ours as well as home improvement stores like Lowes or Home Depot. You can read more about RO systems on our blog “So, You’ve Got Questions About Reverse Osmosis Water?

  3. avatar

    We have well water with an RO and water softening system. Should I use the straight well water, softened water or the RO & softened water to start my new freshwater tank for glo-fish? I’m confused as to which is best and if I still will need to treat the water with anything

  4. avatar

    Hello Dana, That would depend on the water parameters in your well water to start with. Not all well water is the same; the pH, hardness and even phosphate and nitrate levels in the water will vary depending on your area. I would recommend testing your well water right out of the tap to see what your starting hardness, pH and phosphate levels are to start with. GloFish will need a pH around 6.5-7.5 and soft to moderately soft water. If you use water from a water softener, you can generally use that straight into the tank. If you use water from an RO/DI unit, you will need to use a product like RO Right to add some minerals and buffering back into the water since the unit removes all of this.

  5. avatar

    Thank you so much for your reply! I bought a ph tester to check it out. You have been very helpful!

  6. avatar

    Glad to help, Dana. Enjoy your GloFish!

  7. avatar

    I have gouramis and my tank is smelly and brown can you help?

  8. avatar

    Hello Andrea, Aquarium water that is brown and smelly is usually a water quality issue but I would need more information to help you figure out what the best next step is for you. How big is the tank? How many gouramis are in it? How long has it been set up? How often do you do water changes? Have you tested the water quality and what are the result values for Ammonia, Nitrite, Nitrate, pH and temperature to start with? Do you have carbon in the filter, and if so, when was the last time you changed it? I would recommend getting that information together and giving our Fish Room staff a call at 717-299-5691 so we can help you address your tank more specifically.

  9. avatar

    I have a 3 gallon tank with a Betta. I am looking for a stable water source/solution. I have been using Spring Water and, as you noted above, I am seeing fluctuations in pH, hardness, and alkalinity.

    I am interested in using distilled water because I’d be starting with pure water. I would know exactly what was added to it. If I added a product such as Seachem Betta Basics or Seachem Liquid Neutral Regulator, would that solve the problem of pH fluctuations with distilled water? I also use Flourish liquid, Fluorish Excel liquid, and Fluorite–all of which would add micro and macro nutrients to the distilled water. Would this work? Or would I be better off sticking with tap water?

  10. avatar

    Hi Christina, A product like Kent Marine’s RO Right would be a better choice to remineralize distilled water. Both of the other products you mentioned will help buffer the pH but won’t raise the hardness which is necessary to stabilize it. They both also contain phosphate salts which can raise your phosphate (and algae) levels.

  11. avatar

    Great article; very informative and helpful!

    I am a beginner. I have a 40 gallon tank with four glo-fish and one platy. Chloramine is added to my city water. I can buy RO/DI water from my local pet store however it is a distance away from my home. So, would it be possible to use a water conditioner, such as Prime, to remove the chlorine and chloramine; would this make the water safe for the fish? Are these types of water conditioners effective at removing such chemicals from tap water? Thanks!

  12. avatar

    Hi April, Products like Prime will help condition against the chloramine. They don’t entirely remove it but they bind it into a less toxic form until the natural cycling of the tank can get rid of it. Be sure to check whatever conditioner you are choosing since not all of them will remove chloramine. They won’t remove any other chemicals from the water. Another one of our blogs, Treating The Treated – The Line Between Tap Water and Aquarium Water – goes into this topic in more detail.

  13. avatar

    Hi I have a small 5 gallon Betta tank and he does not seem to be doing well at all he is very inactive and just sits at the top and I’m wondering if it’s because of the water. I used tap water with tetra Betta safe conditioner and I’m wondering if I should use spring water, tap water or distilled water? Help I’m so confused lol!!

  14. avatar

    Hello Casey, Bettas aren’t extremely active to begin with and will spend a lot of time at the surface so there may be nothing wrong. They will also go through periods where they will be less active than other times. Testing the water to make sure it is safe for the betta (pH, Ammonia, Nitrite, Nitrate to start with) is always a good place to start and make sure that the water temperature is consistent and within a safe range since temperature can change more easily in a small tank. If your tank doesn’t have a filter, the water should also be changed at least weekly. The BettaSafe should make your tap water safe for the betta by neutralizing the chlorine and chloramines in it but spring water is also safe. I would avoid using distilled unless you buffer it before use like we discussed in this blog. Our Betta Species Profile and Care Guide may help you with some information on caring for your betta.

  15. avatar

    I have been flailing trying to cycle my tank (which is an aquasprouts setup for aquaponics)… I had tested water before fish and levels were all correct, so as a beginner, figured my tank was cycled, so I got fish (6 serpae tetras) which seem to be quite happy so far. Should mention that the local fish store suggested adding some nitrifying bacteria, which I did. my water started out marginally hard but now seems to be at the extreme hard level with pH remaining stable at 6.5. This morning I noticed the NO2 level has risen to 1. I initially used my Berkey water filter (which filters out chlorine and fluoride, but keeps minerals intact) to fill the tank and when hardness seemed to be a problem, I changed the water out 50/50 with snow. In a quandary as to what my next step is. RO water is only available at one shop locally, and a little on the expensive side, so think I will check out the spring water option. Comments?

  16. avatar

    Hello Gail, I would recommend reading through our blog “The Nitrogen Cycle and Conditioning Period in New Aquariums” and our article on The Nitrogen Cycle to help understand at least part of what is happening in your tank. A tank hasn’t even started cycling until fish or a nitrifying bacteria supplement are added and would usually take about 3-8 weeks after that, depending on the size of the tank and bioload. A spike in Ammonia, then Nitrite, then Nitrate is completely normal during this period.

    As for the hardness, what is the General Hardness (GH) or Carbonate Hardness (KH) in this tank and in your source water, what pH are you trying to reach or what are you looking to keep in the tank? Hardness makes it very difficult to change the pH and if it is coming from your source water, it will be difficult to alter. Water softeners and supplements may help or you can look into installing your own RO Unit in your home to produce your own much cheaper than purchasing it. Also, what kind of decor, substrate or rocks are in this tank? Certain kinds of rocks and minerals will raise pH or buffer hardness and if any of these are in your tank, you may need to replace them with something more inert.

    You can contact our Fish Room staff at 717-299-5691 or 888-842-8738 if you would like to discuss your tank in more detail with a member of our staff.

  17. avatar

    Thank you so much for your help. The water from my Berkey is GH 180; KH 120; pH 6.5; NO2 0; NO3 0. I am a little more encouraged after the weekend as the pH has risen to 7.0, the KH is down to 80 (which I have read tetras are happy in) and the fish still seem to be healthy, happy, and active so far. Thank you for the articles which you mention; I will refer to them often I am sure before I finally *get it.* Thanks so much

  18. avatar

    Hi I have three glofish on 10 gallon tank, petsmart recommended me to use distilled water for tank, I have water softer and tested , too much salt PH. It was 9.0 salt pH, so now I’m using distilled water from target, fish looks okay but doesn’t move….

    Do I need water conditioner? Can I use tap water from house which is high salt PH?

    I’m very confusing now, petsmart told me to use distilled water but other said Do Not Use distilled water, it kill fish….

    What do I supposed to do…?

  19. avatar

    Hello M, I do NOT recommend using distilled water. Distilled water has all trace elements and minerals removed so the pH and hardness can fluctuate way too much to be safe for your fish. I’m not sure what you are specifying as “salt pH” but a pH of 9.0 would be far too high for GloFish. I would recommend using spring water instead of distilled or if you used distilled water or Reverse Osmosis (“RO”) filtered water, buffer it first with a product like Kent Marine’s RO Right to remineralize it.

  20. avatar

    Needing help??? I just filled up my 20 gallon aquarium with tapwater is it safe to just let the filter run in the tank with no fish for a week then put my fish in there will the water be safe and all the chlorine be out of the Fish tank by evaporation

  21. avatar

    Hi, the ph level of our well water is high and we do have a water softener but it’s still hard. You recommend a RO system but that might reduce our water pressure. I want to put my Betta fish in a 10 gallon tank. He’s in a 3 gallon right now. I’m thinking the only water I could use is spring water but they are all different as well. What brand name do you recommend to use? Labrador has a demineralized product. Does a Betta need some minerals in their water? I’m so confused and I need help choosing the right water for my little Betta Simon. Thank you

  22. avatar

    Hi, I want to move my little Betta Simon to a 10 gallon tank from his 3 gallon tank and right now he has special Betta water but with the 10 gallon tank I will need to get different water because his special water is in small bottled water. We have well water with a water softener and it has a high ph level of 11. I know Bettas need ph levels between 6.5 to 8 and 7 being neutral would be best. I want to get bottled spring water and I’m wondering if you would know which one would be best. Do Bettas need some minerals, I know they can’t be in chlorinated water right? What type of water is best?

    Thank you,


  23. avatar

    Hi Celine, thanks for commenting! You could use an RO unit. It would give you ~99% pure H2O water, which would be free of the dissolved minerals that cause hard water. Whether you use RO water or distilled water, you would want to ‘re-mineralize’ by adding the good things that are present in water (electrolytes, etc…) that are removed by those filtration methods. Thanks!

  24. avatar

    Hi Celine! You could use water from your faucet and as long as your fish are acclimated to that water properly, they *should* do alright. But if you want to take the next step and provide them with the best water possible…then using distilled water or water from an RO unit would be best. Those types of water are filtered to remove any and all dissolved content, to the point where you have near 99% pure water. When using these types of water it is also important that your fish are acclimated to them as well.

    These are good for removing the bad stuff from water, but they also remove the good stuff like electrolytes and minerals as well. If left alone, your betta would likely survive in this water, but may become lethargic without the pep those elements provide. That is why it is important to add something to re-mineralize or re-energize the water. We carry items like RO Right and Betta Bowl Plus that add those positive elements back into the water and create the ideal environment.

    We hope that helps, please let us know if you have any other questions. Thanks!

  25. avatar

    Hi Bret, thanks for commenting. If you let the filter run for a week, the chlorine will dissipate on it’s own. If you are looking for an immediate solution, something like Seachem Prime or Stress Coat would work. Thanks!

  26. avatar

    Hi thatpetblog, the RO system is not an option for us. Apparently it lowers water pressure. I said that our water is hard but it’s not. The water softener corrects it but our ph level is too high for our Betta. If I want to get him bottled spring water I would have to check the ph level of the brand name but do I have to add a water conditioner and water bacteria in that kind of water for our Betta? Can you recommend a kind of bottled water for my Betta?

    Thank you, Celine

  27. avatar

    Hello Celine, We wouldn’t be able to recommend a specific brand of spring water but most brands should be fine for your betta. The water conditioners recommended in our last reply should be fine for you to remineralize the spring water if needed but always be sure to acclimate the fish to any new water sources carefully.

  28. avatar

    Thank you Eileen. And how do I acclimate my Betta? Petsmart suggests I place him in a bag with his existing water and let him sit in the new tank with the new water for a few minutes. Thank you

  29. avatar

    Hi Celine, Floating the bag only acclimates the fish to the temperature but not to the water chemistry. You can visit our website to view our full recommended Acclimation Procedures.

  30. avatar

    I recently bought a beta fish and was wondering if it is safe to use reverse osmosis water in my 5gallon tank.

    Please get back to me soon.

  31. avatar

    Hello Matt, RO Units are good for removing the bad stuff from water, but they also remove the good stuff like electrolytes and minerals as well. If left alone, your betta would likely survive in this water, but may become lethargic without the pep those elements provide. That is why it is important to add something to re-mineralize or re-energize the water. We carry items like RO Right and Betta Bowl Plus that add those positive elements back into the water and create the ideal environment.

  32. avatar

    Got a new fish tank for goldfish. All of them have died with in the day. We use tetra easy balance and let the filter run before we put the fish in. I know we have well water and thats all i know. What can i do before we get more fish

  33. avatar

    Hello Candis, I would need some more information before I can answer that question for you. How large is the aquarium? How large were the goldfish and how many did you add? How did you acclimate the fish before putting them in the tank? Have you tested your well water, and to start with, what were the values for hardness, pH and temperature? It isn’t unusual to lose fish in a new tank (see our blog “The Nitrogen Cycle and Conditioning Period in New Aquariums”). Goldfish produce a lot of waste and can exaggerate these effects, especially if the aquarium is very small or the goldfish are large. Also, if the fish aren’t acclimate to the tank properly, they are less likely to be able to handle the stress and shock of a new environment (see our recommended Acclimate Procedures for more information). If you would like to speak with someone about your tank in more detail, you can reach our Fish Room staff at 717-299-5691.

  34. avatar

    I have a 50 gallon reef aquarium and currently do my water changes using distilled water. It is such a pain to buy and lug all those jugs of water around. I thought about an RO system but I believe it produces a lot of waste water and most of the ones I have looked at for my aquarium, say not to use it for drinking water. I’d really like to be able to use whatever system I buy for both my aquarium and for drinking water. Have you heard of the Berkey water filter/purifier? This seems like it would do both but I’d like another opinion before I invest in it.

  35. avatar

    Hello Shelby, RO units will produce some waste water but it shouldn’t be “a lot” by any means. If the unit is producing a lot of waste water, there is likely something wrong within the unit or membranes. The RO Units that we sell for aquariums are generally speaking the same units sold for home use for drinking water. Most RO Units will not advertise water as being safe for human consumption because all of the minerals and trace elements have been removed, not because the water is necessarily toxic in any way. I’m not familiar with the brand you mentioned but if water is safe to drink, it should be safe for your aquarium but every unit is different and you will want to take into consideration the membranes and type of filtration used in the unit as well as the water source you are filtering. For more information on RO units and membranes, check out our blog “So, You’ve Got Questions About Reverse Osmosis Water?“.

  36. avatar

    I have a 10 gallon tank I have tried everything to stop the water from turning green I had the water tested at the pet store the tank only stay clear for about 2 weeks

  37. avatar

    Hi Stephanie, Have you tested the Phosphate level? Green water is a classic sign of high phosphates. In addition to testing the level in your tank, I would recommend testing the level in your source water as well (ie. out of the tap if you are using tap water). Some areas have high phosphate levels right out of the source, especially if you are using well water or in a highly agricultural area. If you discover you have high phosphate levels after you test, there are different types of filter medias that you can use to help eliminate it, and you may want to change your water source if those levels are high. Also, making sure your lights aren’t too long should help control the algae; stay below about 8-10 hours.

  38. avatar

    hello, my oldest(4+ years) KOI died last night … a little later my goldfish did the same , I quickly removed the three remaining KOI out of the 20 gallon tank and this am started the cleaning process. I use city(small town) water and am considering “SPRING WATER”. I do use purifying chems minimally with the right measures …. SPRING WATER good ? my largest KOI is 9+ inches the smallest is 2-3″ …. I do not want them to go “BELLY-UP”… help wanted

  39. avatar

    Hi Tracy, A 20-gallon tank is really too small for even one goldfish and definitely not for any koi. Koi need large ponds especially and shouldn’t be kept in an aquarium unless it is at least a few hundred gallons. Dechlorinating tap or municipal water will help – make sure to get a dechlorinator that neutralizers both chlorine AND chloramines – or spring water will be suitable as well but neither will make much of a differences in an overcrowded aquarium.

  40. avatar

    Hi, I have well water that ph comes out of tap at 8.2 and after an hour or two ph drops down to 7.0 , I worry about the ph dropping so quickly may hurt Betta. My tank is 3 gallon and I was using spring water but it got to be expensive for all the water changes. I would leave well water sit out for awhile before adding it but our house gets cold and I try to add same temperature water as tank which is 78 F. Do you have any ideas on what I can do about the high PH right out of tap?

  41. avatar

    Hello Tyra, What is the water hardness? If the pH is fluctuating that quickly, I would guess that your water is pretty soft, meaning that it has no buffering capacity to stabilize it. Adding a buffer to raise the hardness and buffer the pH would help.

  42. avatar

    Thank you SO MUCH for your reply, this has been pretty frustrating to me as you can imagine lol. I don’t want to add in 8.2 ph water so I’ve been adding 2 drops of ph down to water that I add which isn’t really good idea I dought, to try and make ph closest to aquarium water 7.2 , when adding and then someone told me to add a little baking soda couple hours later to keep it from going down too low. So it goes down to about 7.2 and stays there until next water change. I don’t know what else to do to lower ph to match aquarium water during water change. I’ve done water test in bucket and it goes from 8.2 to 7.2 in a few hours on its own with no additives. I only use Prime in aquarium and keep tanks very clean. I’m not sure what the tap water hardness is, is that the gh and kh? Should I get a test for that and how do I buffer the water that comes out of tap without using ph down, I would like to stop using that. My poor fish! Lol

  43. avatar

    Hi Tyra, Adjusting the pH before you put the new water in your tank is a good idea. I would definitely recommend testing your tap water hardness so you know how best to adjust it. GH and KH are both important, but KH is going to play a bigger factor in this situation for stabilizing the pH (the “buffering capacity”). If your KH is low, you can use a buffer like SeaChem’s Neutral Regulator or Alkaline Buffer to help stabilize it. In my experience, these products work more reliably than ph Down or pH Up to stabilize hardness and pH.

  44. avatar

    Ok, thank you so much! You have been such a big help!

  45. avatar

    Hi I’m wanting to set up a small tank with some good fish and bubble eyed gold fish I was wanting to know what type of water I should use .

  46. avatar

    Hello Faith, Goldfish should have a pH between 6.5-7.8 consistently. They also need a large, well-filtered tank to be able to handle the amount of waste they produce and don’t do well in smaller aquariums. This Goldfish Species Profile from our website and these other Fancy Goldfish articles from our blog may help you.

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About Eileen Daub

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Marine Biologist/Aquatic Husbandry Manager I was one of those kids who said "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and in other local roles. If that isn't bad enough, I'm a proud Crazy Hockey Fan (go Flyers and go Hershey Bears!).