New tank: pH keeps rising back up to 8.1~

[Martox]

I plan on keeping Discus and I made my own 5'7" tank to keep them in. I'm about 2 weeks into fishless cycling the tank, and I notice my water rises up to around 8.0 pH whereas my tap water is at 7.2 pH. I've done water changes twice now and it still rises back to 8 without fail. My substrate is Marine Pure Biofilter balls and Bio balls, any ideas as to why this is happening?

[Akili]

What is the material used to make the tank? Is it a bare bottom tank? Are they any item in the tank like pots or decorations and gravel?

[Martox]

What is the material used to make the tank? Is it a bare bottom tank? Are they any item in the tank like pots or decorations and gravel?

Sorry should've been more detailed.
It's made from glass. Yes it's a bare bottom tank, nothing in the tank besides media and 2 bags of established filter rock from my pond.

[Cosmo]

I plan on keeping Discus and I made my own 5'7" tank to keep them in. I'm about 2 weeks into fishless cycling the tank, and I notice my water rises up to around 8.0 pH whereas my tap water is at 7.2 pH. I've done water changes twice now and it still rises back to 8 without fail. My substrate is Marine Pure Biofilter balls and Bio balls, any ideas as to why this is happening?

Most likely culprit is disolved C02 in your source water. As you aerate it, the C02 is driven from the water and the Ph raises. Had the same issue with my water. Only way around it is to age your water 12 to 24 hours before adding it to your tank. As a way to test if this is your problem, partially fill a 5gal bucket with water, measure the Ph, then leave an airstone bubbling away all night and test your Ph again in the mornig - I"m betting it's higher just like what you're experiencing in your tank.

[Akili]

Test the filter rock for Alkalinity perhaps that is the causing the raise of pH