How to prepare my RO water

[davidgallar2]

I have an 10-gallon nano but every time I change the water the ph drops a lot because the RO water has no minerals. This is affecting my aquarium a lot. I tried to raise the ph with a buffer before using it but now my KH is super high and the PH is low. What do you recommend me to do?

 

[Randy Holmes-Farley Verified Community Expert]

Let's back up, since your observation is unusual and unexpected (and may be a test issue).

Adding absolutely pure fresh water to seawater raises pH for complicated chemistry reasons. There's NO reason to add anything to top off water.

Is the water you are using 0 ppm TDS?

It may have collected some CO2 from the air, though that is unlikely to impact pH appreciably.

Are you measuring pH near where the water is added? The salinity change as water is passing by the probe may impact the measurement without indicating an issue for the tank pH overall.

How much added fresh water are we talking about in percent of the tank volume?

After the new water is mixed in, is the pH lower? From what before to what after?

 

[Randy Holmes-Farley Verified Community Expert]

Never use buffers to boost pH unless you know you also need alk. There is no chemical additive that can boost pH and not alkalinity.

If you add a lot of fresh water and lower the alk, and then allow it to re-equilibrate with the room air, the pH may decline, reflecting the alk lowering and the way alk impacts pH.

FWIW, pH 7.9 is fine. .