Hello! I have a fluval aquaclear 20 power filter in my 20h aqueon tank and I was wondering if I should really be using an air pump? I have been using one per pet store employee recommendation and it appears that it is making it very difficult for my Cory catfish to swim. They have been lying still a lot ever since I installed it and are active again now that it's turned off. Thoughts? Is it really necessary for circulation when I have air at the top of the tank and holes in the lid?