ph what is the cause

[springer]

I have a 55 gal. tank with 2 discus ( mated pair) I am now trying to return the water from original tap water back to soft water using my ro unit. This is because I have removed the fry at 3 weeks of age and will try to have the pair mate again. I have been doing 25% water changes per day. The ph to begin with was about 7.5 the ph of my ro water is 6.5. When I add the new water the ph will go down to about 7.2 and I thought over a period of several water changes the ph should eventually hit 6.5. When I test it the next morning the ph reads 8.5 and then will level off at 7.3. I can't seem to get it back to 6.5. The fish show no stress and are doing fine. The tds has been coming down from 250 and now is stable at 75. I can't understand the rise in the p.h. Any info would be appreciated. Thank you.

[Richy44]

When I test it the next morning the ph reads 8.5 and then will level off at 7.3.

Is the PH of 8.5 after you do a water change? If so,

Do a test. Fill a glass of water straight from the RO. Test PH
Next morning Check PH of the water.
Does it follow your scenario. High out of the RO and after aging drops down?

If you age your water overnight in a container with an airstone running hard, this will precipitate the Co2 and bring the PH down before adding to the tank.

This will stop the PH swings.

Hope this makes sense!

Cheers

Rick..