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I'm getting a RO system for my aquariums and will be transitioning slowly to completely RO water. I've got a planted, 29 gallon tank, and dose daily with Excel Flourish rather a CO2 system. I've got a TDS meter, and both a Gh and Kh test kit, plus Seachem Equilibrium and both the alkaline and acid buffer. What I'm wondering is what levels I should be shooting for in the RO water and the right sequence in which to treat the water to achieve those levels. I'm new to this and would like to start out right and not just guess about it or have too much trial and error.
 

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Research the fish or shrimp that you would like to keep.

If your tap water is reasonable, just too hard, then you can blend RO + tap to make the correct levels of minerals to suit the fish or shrimp. If the mineral levels are still not quite right you can add just a few of the ones that are low or missing.

If the tap water has some problems and cannot be used for aquariums and you will be using pure RO then you will have to add all the correct minerals in the correct ratios.

GH is a test that shows calcium and magnesium, combined. This is the most important parameter for fish.
Starting with RO water, add GH booster, which is a combination of calcium and magnesium, and often potassium. GH is measured in German degrees of hardness, and in parts per million (which is the same as milligrams per liter).
Soft water fish would prefer a GH under about 10 degrees, though the optimum value should be researched for each species.
Hard water fish would prefer a GH over 10 degrees, again, research the fish.

KH is a test that shows how well the water resists changing pH. The term for this concept is buffer- a material that will stabilize the pH at a particular level. The most common buffer in aquariums is carbonates and bicarbonates. KH (carbonate hardness) is also measured in German degrees of hardness, parts per million and milligrams per liter.
To raise the KH in the water you can use baking soda or potassium bicarbonate. Add just enough of one of these to make the pH correct for the species of fish or shrimp you want to keep. Initially, you might start by making the KH equal to the GH.

If you are keeping fish that come from a rain forest river with a lot of fallen leaves that contribute tannic acid and other organic acids then you can add some peat moss to treat the water, and in the filter, in a bag (I use a nylon stocking), driftwood in the tank, or any of several other materials. This will lower the pH. This type of water is referred to as Blackwater.

Here is how I handle this:
1) For soft water fish I run the water into a garbage can that is dedicated to fish use. Depending on the fish requirements, this can be any sort of blend of reverse osmosis and tap water. For black water fish I add a knee-hi stocking of peat moss. Then I circulate the water with a fountain pump to be sure anything I have added is well dissolved, well blended. If the water is for fish that prefer warmer water I will add an aquarium heater, hanging it in the middle of the water flow. I add dechlorinater when I use tap water.

2) For harder water fish I will start with tap water and add the right balance of GH booster and baking soda so the GH suits the fish, and the KH will stabilize the pH where the fish want it. Like the soft water blend, I also add dechlorinator and circulate the water with a pump, and heat it when needed.

If there is an established tank with livestock, and you want to make the water softer or harder to better suit the fish make such changes slowly. It takes time for the fish metabolism to adjust to changing mineral levels. It may take several weeks or a month to alter the water.
 

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I'm getting a RO system for my aquariums and will be transitioning slowly to completely RO water. I've got a planted, 29 gallon tank, and dose daily with Excel Flourish rather a CO2 system. I've got a TDS meter, and both a Gh and Kh test kit, plus Seachem Equilibrium and both the alkaline and acid buffer. What I'm wondering is what levels I should be shooting for in the RO water and the right sequence in which to treat the water to achieve those levels. I'm new to this and would like to start out right and not just guess about it or have too much trial and error.
When you say you're new to this; do you mean new to the hobby or new to using an RO system? What makes you think you even need an RO system?
 
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