Water for fresh water tank

Midnight

Member
I'm starting a 15 gallon FO fresh water tank. I have a RO/DI for my reef tank but I thought I read somewhere were the RO/DI is too filtered for fresh water fish is that true? And if so what do most people do to get water ready for a tank.
 

SubRosa

Well-Known Member
Use a product such as Prime to remove any chlorine/chloramine if present. If you're on your own well, no treatment is necessary at all, beyond perhaps letting it stand overnight. Often water from a well is rich in CO2 so it initially will have a very low pH. Upon standing in air and reaching CO2 and O2 equilibrium with the atmosphere it can be much higher. A friend has water out of the ground at a pH of about 5, but when it stands for a day the pH rises into the high 7s. The only time I use RO in a fw setup is to top off for evaporation, or since my tap water is fairly hard, if I'm dealing with a very limited number of species which truly require soft water to live and/or breed. Other than that, most common species can adapt to almost any hardness level and you're better off to just change more water rather than trying to make it "perfect" for them.
 

whippetguy

Well-Known Member
RS STAFF
PREMIUM
I use tapwater treated with Prime and let is sit in the bucket for 24hrs before use. My city has a pretty good water supply, though.
 

DaveK

Well-Known Member
While you can use tap water treated with prime, you can still have issues. Sometimes local water has way too much in the way of nitrates and phosphates, or has some other undesirable qualities such as being way too hard or soft for the fish you want to keep.

Since you already have the RO/DI unit for SW, you can do what I do. Use the RO/DI water as a base and adjust the pH, DH and KH to be exactly what you want. I found I got much better results, especially with such things as planted tanks. Usually I want the GH about 8 and the KH about 4.
 

ddelozier

Well-Known Member
PREMIUM
RS Ambassador
It depends more really on the fish you want to keep. some like softer water. 7 which is neutral, is generally soft enough for most fish. If they need softer water, add a half tablespoon per gallon of aquarium salt(FW aqaurium salt only here, marine salt wont work). If they need harder water, Add a little boiled baking soda or commercial DKH prducts. RO/DI water will work find for FW, and if you do it that way, adjusting the PH as needed, you wont have as many problems with Algae(at first). Most municipal water supplies and some sources of well water, have detectable nitrate/phosphates(algae food). Fish waste naturally breaks down into these things, so whether you have problems later depends on husbandry and filtration.
 

blackbeltmom

Well-Known Member
PREMIUM
I have also been told that you can use the waste water from your RO for your freshwater tanks.
I also didn't think it was the fish that liked the dirtier water, I thought it was plants when you are trying to have a planted tank.
 

blazend

Member
I use RO/DI with my freshwater tank. I have always done this cause i keep discus fish and they need very low GH/KH. I like to keep one bucket of tap water on hand that i use prime on. I use this for top off.

So RO/DI water for water changes and tap water with prime for top off. I have always been told to splice my RO/DI water so this was my method of doing that with using a very limited amount of my tap water because its in the 400+ range when i test it with my TDS meter.
 

Dracko

Well-Known Member
The bottom line here is that it depends on your water. Most tap water + prime is fine, but some places are not. I live in Salina Kansas. and my tap water had Chlorine levels that were 20% higher than used in a swimming pool. After analysis I found 15 other bad chems in the water:confused:. So I bought a RO whole house system. If your water smells funny or looks funny have it tested. Many places that sell softener systems will do it free (you may have to hear their pitch) and will check for things your LFS may not. But never add tap water to tank (top off) without letting it sit for 24 hrs first.
 
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