Planted Tank Guru
Join Date: Nov 2009
Location: Missouri united states
Will need to reduce hardness to move pH down.
This can be done with mixture 50/50 of R/O water and tapwater mixed and stored in large tub or barrel which you would need to do to have same water available for water changes so as not to shock the fishes with sudden change at water change time.
Do you know what the pH from the tap read's ?
In all honesty,,If the fishes are doing well, I would not mess with trying to adjust the water at this point.
Are you sure you have playsand and not contractor's sand which might contain mortar/lime?
No rocks in the tank's that might contain limestone/calcium?
Could test pH of water from the tap after sitting in bucket,jar,pitcher,etc for 24 hours,then add some of your substrate to the container of tap water and test the pH again after 24 hour's.
If the pH is higher than the tap after 24 hours ,then something in substrate is causing the pH to climb higher than that which comes from your tap.
Can do same thing with any rock décor and small bucket of tapwater.