Hi, about 2 years ago I set up my 60L tank and it’s been running since then. However I never really put enough gravel in, only about 2cm thick which probably explains why the plants didn’t grow very well. Anyway, I’ve ordered a mix of potted plants and was going to buy some more aquarium gravel. Would I be ok just adding fresh gravel on top of the old gravel or will this affect the B.B.