Switching to RO water

[SNPiccolo5]

I am soon (this weekend) going to start using RO water for the 55 gallon tank. I was thinking about different ways to do this that all end up with the same end result. I am planning on using 1/2 RO water and 1/2 tap water, I really don't have the $ to do all RO water with my water changes...

I was wondering that if I empty my tank half way and then fill it up over a period of 3-5 days, would that be too much of a pH shock for the fish, and is it OK for the tank to run half-filled for a time? I definitely am not going to just replace it with RO in one "fill" since that would be a huge pH shock (my pH out of tap is above 8.5). Also, I am not going to do continuous water changes since it is less effective and I want to get the parameters changed safetly in the tank ASAP.

-Tim

[m.lemay]

Is your co2 system working with the ph controller ? If it is your controller will keep the PH relatively stable if you add your RO water into the tank slowly and let the Ph stabilize. The nice thing about the controller is that it gives you instant Ph readings. A ph variation of .1-.2 shouldn't make any difference as its getting mixed in with the tank water. I think you can add the RO water over the period of 4-6 hours with no ph shock with your controller regulating co2 to adjust for ph.

Marcel

[lanstar]

If you test the pH of pure RO, you may find it varies significantly from your current pH. But... if it's good RO water, its buffering capacity should be near zero. The ion balance in the remaining tap water should work to keep the pH at or very near its current level. The concentration (KH) will go down, but the balance between acid/alkaline ions in the mixed tap/RO water (and thus the pH) should not significantly change.

If your pH is 8.5 with pure tap water, which I'm assuming has pretty high GH/KH values, a 50/50 mix will also have a pH very near 8.5 and GH/KH values about 1/2 of what your pure tap water has.

If you're wanting to lower your pH, it will be easier to do with a 50/50 mix. You won't need to add as much acid. If you want to do that, I'd suggest using an acidifier made for Discus tanks. They contain no phosphate. "Amazon Acidifier" or "Discus Buffer" are two examples. They use HCl (hydrochloric acid) to lower the pH and contain no phosphoric acid.

Good luck!

Tim

[SNPiccolo5]

I do use my pH controller, but the only problem would be that the probe would not be deep enough in the tank if I emptied half way, also my reactor is set up so that is stops working after the water goes below 75% full in the tank. I was planning on leaving the CO2 off when I did this change.

I think the pH would not just stick at 8.5 or above because the RO has organics in it (and yes, its KH checks at near 0; traces) which make it acidic (its pH is 6.4) and when you are adding the RO to the water, you are also taking away some of the KH of the tap water, I checked and its KH is near 7, which is still medium, but not near what it used to be... However, the pH may remain at 8.5, which is of little importance since the KH does go down.

My main concern is getting the KH low enough so when I add CO2 the pH drops below 7. At KH 8, the CO2 is 35 ppm when the pH is 6.9 and at KH 7 the CO2 is close to 31 ppm when the pH is again 6.9. Is 35 ppm too much for the fish? I know that 4-6 KH would be ideal, but I want to see how this works. Thanks!

-Tim

[lanstar]

Originally posted by SNPiccolo5
However, the pH may remain at 8.5, which is of little importance since the KH does go down.

My main concern is getting the KH low enough so when I add CO2 the pH drops below 7.

If that's your concern, an easy way to ease your mind would be to simply mix up a very small test batch of 50/50 water in a jar... let it sit for an hour or so (to let the ion balance that regulates pH re-establish)... and test the parameters (GH/KH/pH) of your test sample. Then you'll know, very closely, what you're going to get before you go "all the way" and change your tank water.

You may find that the GH/KH in your tank ends up a little bit higher than in the test sample after a day or so IF there are items in your tank/filter that have collected "mineral" deposits. With the lower GH/KH, deposits on things (if there are any) could partially dissolve back into the water. However, after a few water changes, this process should stop.

Good luck!

Tim