Mixing ro and tap water.

[Hf21]

Hi all my tap water is hard (ph7.8,gh around 20, kh around 4, tds320) so i'm going to run one of my tanks (Cory's mainly duplicareus and gold laser) half tap half ro to bring the values down. My question is if I just replace half the water for ro i take it the ph dropping and hardness dropping instantly would not go down well and could crash everything. How do I go about doing this safely for the fish? Remove half the water and drip feed the ro into the tank over a few hours and then after that water changes could just be done with it ready mixed as they would be acclimated.bor do small percentages of ro over a few weeks? I dont want to send them into shock over the values rapidly changing.

 

[seangee]

If you add your water at the target ratio you will be fine. By this I mean if your target is 50/50 and your remove 50% of the water, replace it with water that is already mixed to 50/50. That way you are only putting in 25% RO on day 1 or reducing your GH from 20 to 15. Your second change would reduce it from 15 to 12.5 and so on. In theory you won't ever reach 10 but in practice you get there within a month or so. If it makes you feel better you could do 2 x 25% changes in week 1 but it isn't actually neccessary.

Just FWIW ignore pH and TDS and let them go to wherever they end up. I use 100% RO in my South American tank. GH 0, KH 0 and pH below 6. TDS is only useful for determining if the RO membrane and filters are still doing their job.

 

[kamanut]

My RO has the same pH as my tap water, so maybe check that. I mix about 30% tap water (ph 8.4, KH 38, GH 1, TDS 1000+) with my RO (8.4 pH, 0 KH and GH, 10 TDS) in my tank. I just keep an eye on GH and add Equilibrium to bring the GH up (have hard water fish) when I do a water change.