welcome to fishlore kquaz!! although the snails are awesome, and keep the tank very well clean, they can overstock in no time...maybe snail control with some lettuce, and removing them periodically, will help..and sell them to your
LFS or on aquabid? alot of fish eat them, but in a 20 gal tall, not many will be the bottom dwelling snail eaters for that size..maybe some other members have some suggestions, but the space is limited in a tall tank and pretty much your 3 spot is going to outgrown and not tolerate much more in that size tank...its evident already if your glass fish are hiding...hes not playing nice in the playground....
ph isnt as important as long as its stable...most fish will
acclimate to all different kinds of ph's as long as its done slowly...there are those type of fish that do require a certain ph to thrive in , eg africans, loaches, goldies etc, but for the most part it shouldnt be an issue...hope some other members have some more bottom dwelling help for you and your snails!