Yep, I'm not familiar with substrate depths for specific fish - but there are some guidelines for planted tanks, that they should have deeper substrates to keep the plants down (2-3 inches). But even that is just a guideline and not always necessary. Also, some tanks have a sloping substrate - with deeper substrate in the back of the tank and shallower in the front.
25g Marineland Eclipse (30w T-8 ):
- java ferns, anacharis, corkscrew vals, giant hygros, marimo balls, java moss
- zebra danios (5), otos (2), others TBD
6g Marineland Eclipse (8w T-5):
- anacharis, asian ambulia, java moss
- white cloud mountain minnows (10 = 6-7 inches total)