cant get PH down

[crx2ner]

so I have a 20g long "frag" tank. Its only got a few zoas in it as of now. its been up for maybe 2 months. It had a high ph all last week, so I did about a 50% water change yesterday. I just checked it and its still at 8.8. I’ve got 2 HOB filters (2 compartments each) with carbon and gfo in 1, and a "1/2 unit" of chemi-pur, some filter flow and a ball of cheato.

 

Its bare bottom, and I’ve got about 15ish pounds of rock. as for as live stock other then snails and 3 blue legged hermits there isn’t any.

 

before doing the water change i was using kent ph buffer which says it will maintain the water at 8.3 but it apparently didnt work?

 

any suggestions on how to get this down?

[amnestia]

What's your alkalinity at? Are you sure your test kit is reading correctly? get a confirmation with a LFS

[Amphiprion1]

If you can confirm test kit results, try heavily aerating the water and see what happens--it should help drop it to a manageable level slowly and safely. Another water change with aged water (without buffer) should help, too.