Is this a picture of your 75 g? You have nice plants, but you should definitely add some substrate. One, it will help to keep the humidity. Two, it will be perfect for springtails, which your frogs will love, and the microfauna will not be able to strive on plain glass. Three: it's better for your frogs.

Also, you could add a drainage layer using hydro balls. Once you have your drainage layer, your substrate, don't forget to add a layer of leaf litter for your frogs.

For your 40 gallon, it's pretty big. Go for some leucs perhaps, or some auratus.

Eric