How much RO needed to be able to reduce GH?

Fish4dawin

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Hey all, I’ve been thinking about using RO water in my 29 gallon tank to help soften my GH so I’m able to have fish such as corys and tetras and so on. Now my question is, how much RO water is needed to bring down my GH. Currently my GH is at 290ppm, meaning I can only really have rainbowfish and African lake cichlids. Do I just need to add the RO water then test the GH, and go by how much it has dropped?

Many thanks,
Ev
 

Colin_T

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You can do livebearers as well, they love hard water.

Reverse osmosis (r/o) water should have 0 GH and 0 KH, with a pH of 7.0. If you mix it 50/50 with the tap water, your GH will be around 150ppm and that is fine for soft water fishes as long as they aren't wild caught.

You can do 75% r/o and 25% tap water if you want it lower, but anything below 150ppm is suitable for most tetras, angelfish, Corydoras, etc.

When you mix tap and r/o water, do it in a bucket and aerate it for 30 minutes before using it in the aquarium. You should dechlorinate the tap water and aerate it for 5 minutes before adding the r/o water.
 

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