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Thread: Tap water to RO
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Old 07-25-2013, 01:14 AM   #4
Diana
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pigeonfood, it depends on where you want to go with this tank.
Most community fish are just fine with such a wide range of water chemistry that it is easier just to use the tap water, unless it has some toxins.

Next, ignore pH.
Get tests for GH, KH and TDS. These are the important values to fish.
Many years ago the old fish keepers only had pH tests, so they blamed everything on pH. Now we know differently.

OK, lets say you test the tap water, and find the GH and KH are way out of the range for the fish you want to keep, and you really do not want fish that are suited to those values. Here is how to handle it.

You have tap water with minerals.
You want to use RO (it has no minerals) but you want to add minerals to the RO.
Why not just use tap water as the source of minerals? Are there some toxins there that make it bad to use?

Get some RO water (a gallon is just fine) and make some blends.
25% tap + 75% RO
50/50
75% tap + 25% RO.
Test all for GH, KH and TDS. Which comes closest to what your fish want? (Hint: Do research on your favorite fish so you will know what the target is).

If one of these is great, but the other is not, use the recipe that makes the softest water and add just barely enough minerals to bring the other value to where you want it. Most fish do fine when the GH and KH are pretty close to the same, but they do not have to be. GH is more important. If the KH is a couple of degrees plus or minus that is just fine.

Then, if you are keeping a fish from a black water river, filter that 'perfect recipe' through peat moss. Peat moss adds the organic acids these fish like.

Test the GH, KH and TDS again. Some peat moss can remove a certain amount of minerals.
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When you want to adapt the fish over to softer water you will have to do some math.
Do a big enough water change, and use enough of the 'perfect recipe' so that the net change results in softer water in the tank, but the GH, KH and TDS drop by no more than 10% in any one water change. Do this sort of water change up to twice a week.
It may take a month to get the water softer and the fish switched over. Let it take time. The fish need to adapt to the lower TDS, and it takes them about a month to do that.
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If the tank needs larger water changes while this is going on, then make a blend of RO + tap that equals the current GH, KH and TDS of the tank, and do as big a water change as you need to. When the GH, KH and TDS are the same, it is just fine with the fish to do larger water changes.
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Now that you have set this up, here is how to handle new fish purchases:
1) Set up a quarantine tank.
2) Buy the fish. Test the water in the bag.
3) Add enough minerals to the Q-tank so it matches the water in the bag.
4) While the fish are in quarantine, slowly alter the water just like you did the main tank until the fish are in water that matches the main tank. Optimum quarantine time is about a month, unless you need to treat for something, and in that month the fish will adapt to your water.
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