Hi, I'm relatively new to marine nano reefing and needs some help. I recently purchased a 14g Bio Cube and am having trouble with pH stability. I have live sand in it and live rock, but the bottom inch or two above the substrate is very acidic, pH around 5.8 while the rest of the tank is stable at about 8.1. I tried using some airstones to increase the circulation near the back of the tank but it doesnt seem to be working. I'm going to try a water change and try siphoning the water out but help is definitely appreciated.