RO water PH issue

[smitty24]

So after many years i have started back up my tank and got some discus. I have kept them for a long time, but in Ohio the water sucks! I am on a well and PH is 8.5+, GH and KH are about 350 - 400 pp, so i went RO water. Out of the RO/DI system i am seeing PH at about 6.0 - 6.5, GH and KH about 15 ppm. When i do a water change the PH creeps over 8.0 - 8.5 in one day. I have tested just RO water with seachems' Equilibrium in a 5 gal bucket with a power head and heater, seeing PH creep after 1 day to 7.5 PH. Any ideas how to stabilize the PH and keep it around 6 to 6.5?

Dosing trails with RO water and Equilibrium.

5 Gal RO water and 1/4 tsp of Equilibrium
5 Gal RO water and 1/2 tsp of Equilibrium

Still seeing PH creep....

[RogueDiscus]

I think the advice you'll get here is to not try to hold your pH at the low mark, but to age your water for a day to let it stabilize, and use it as is. Otherwise you're messing with chemicals you don't need. The experience of most is that discus don't really need low pH, just stable pH. I have similar well water and mix it with RO, but my pH in all my tanks is still near 8.

[smitty24]

I am using 100% room with now and adding minerals back in. So based on the suggestion I should do x% RO and x% tap.

So 90% RO 10% tap?
80% RO 20% tap?

[RogueDiscus]

Kind of depends on what you want. You only need really low tds if you're breeding, usually less than 60 ppm. I keep my growout and adult tanks around 200-240 ppm. Some go even higher. So 50/50 would be fine and you'll use less RO.

[Willie]

100% R/O water has no buffering capacity, so pH readings are not real. When you mix in a little tap water, it goes right back to your original R/O.

The question you should start with is whether your fish is not doing well without R/O. Will your fish grow better with R/O? In most cases, your fish will do best with large, frequent water changes. That's virtually impossible to do with R/O. I would recommend that you up your water changes with regular tap and watch your fish thrive. No one I know has ever seen discus stunted because they're growing in hard water.

As for spawning, that's an entirely different story. You can deal with that when you see the discus cleaning their cone and laying down a mass of eggs.

Good luck, Willie

[DJW]

In an aquarium, the pH is just a side effect of something else— like CO2, KH, or nitrification. Well water usually contains a lot of dissolved CO2 and needs to be aged for water changes, and it looks like yours may need ageing, whether or not it has gone through an RO filter.

I use straight RO, and after the 12 hours it takes for the barrel to fill up from the ro filter, the first water into the barrel is aged, the water that went in 6 hours ago is half-aged, and the last water isn't aged at all. I try to let it aerate for at least 6 hours after the barrel is full before using it.

We measure KH in a linear way and pH in a logarithmic way, so that if you add a small amount of KH to pH 6.3 water the pH will go way up. And if you were to add the same small amount of KH to pH 8.0 water the pH will hardly go up at all.

I agree with Willie that whichever water you choose to use, its best to use a lot of it.