Using RO water

[Nurse4u]

After a lot of thinking and researching I have decided that I am going to start using RO water in my new tank. My pH is 8.4 and even though my water is extremely soft... I think I could put 1/2 drop in and it would change! lol My KH on the other hand my KH is through the roof... Gotta love well water!

I am looking for some suggestions and a little extra first hand knowledge. The RO has a pH of 6.0... in addition I have a fair bit of driftwood in the tank. I have a fair bit of java fern in the tank and a couple swords but no CO2 to worry about bring the pH down further.

I know that I will probably have to add some minerals back to the tank for the benefit of the fish as well as my plants. Currently I am hoping to have a group of Geophagus Tapajis 'orange head' in the tank... However, these fish are very young and small. To add some color to the tank (75g) I think I may put a pair of German Rams in the tank. The person I am getting the orange heads from keeps his at a higher temp (around 82-84) much like the GBR prefer. I am also going to have a school of some type of tetra in the tank.

I want to bring the pH back up to around 6.8-7.0 I think. I have tried just cutting my tap water. If I use 80% RO my pH comes down to about 7.0-7.2 after 48hrs with a air stone in the container.

What are the odds of a pH swing? Am I better off going 100% RO and then buffering so I know exactly how much to add each water change? What products have you found to work best?

Thanks!

[Pete]

RO water doesn't really have a ph of any measurable relevance. It might read 6 but only because your test kit can't handle the truth.

If you're cutting it with regular water, which is certainly the right approach if you insist on using RO to lower ph, then to ascertain the likelihood of a ph swing you need to measure the KH. You can have a ph of 7 with a low KH and tomorrow the ph could be 4. KH gets used up over time by the filter and once it's low enough that's where you get the ph dropping rapidly.

You'll need to take lots of measurements for ph and KH until you have it down to an exact science such that you can know how much RO plus how much well water to change each time - and put the water changes on a regime that keeps the values as constant as possible.

I still maintain that Geophagus will do fine in the higher ph water and it's probably only at breeding time where you might want to consider playing with their water chemistry.

[chris1932]

I disagree, just because the geos will survive in 8.4 doesnt mean they will like it, If they are wild they may not survive the change in osmotic regulation. What is the raw well water tds and conductivity?
I can survive on the north pole, I would not be happy about it nor would I thrive.
Kent RO right at half the recomended dose and Kent discus trace.

Check the tds and pH of the RO permeate. I would be surprised if a household unit got below a tds of 30. You can add a seccond pass to the concentrate stream to reduce water waste.