At first I liked the red gravel but the mix is growing on me.
I see a few problems in your tank though. First of all size, for 4 bettas a 6 gallon is just fine but once you start adding more fish it can get crowded fast. If I where you, I'd put the loach, glass cats, and tetra in a seperate tank. In another thread I saw that you wanted to spawn your bettas, it would be easiest to spawn them without tankmates so having just the bettas (and maybe a dither fish) would be best. But, if your not having problems with amonia or nitrate I think the fish will continue to thrive.
The second is that your loach, glass cats, and tetra all should be kept in schools of at least 3, prefferabely 6. But as you probably know, 6 glass cats, 6 loaches, and 6 tetras would not do well in a 6 gallon for long. The loach also needs at least a 10 gallon tank. Loaches swim allot -as you've probably noticed- so they need lots of room. Especially when keeping multiple loaches wich you might end up needing to do.
I'm also 12 and I know how hard it can sometimes be to have people say bad things about your tank especially when you've put allot of work into it (wich I'm sure you have). But anyway, I love the tank, I love that you started out in the hobby at such a young age, and I wish you best of luck with your tank.