Mystery snail and low ph

[Pearly]

Hi Guys, I'm new to snails but love having them for clean up. They do fabulous job and never seem to bother my live plants (I do drop algae wafers and feed my fish frozen peas few times per week, I'm sure the snails get some of that too. I'll be researching on their diet and stuff but meanwhile one of my betta tanks started dropping ph over time. Just tested last night and it's 6.6. It is heavily planted tank with filter, light, gravel, driftwood and piece of almond leaf which I started using couple of months ago to control high ph. The tank houses male betta and mystery snail. I know bettas adopt to gradual ph changes but the snail is not going to like that is he? Advice? Another think I have 4 other tanks and do everything this same with all 4, this is the only tank where the ph has gone down that low, others are 7.4-7.6. Please offer your thoughts