The only issues with covering the tops of tanks completely, especially as small as a nano, is that proper gas exchange in order to replenish oxygen that your inhabitants use. You can hop over and see Alfredshouse's tragedy due to a lack of oxygen... made me think twice about covering my tank, that's for sure. You should also think about the temperature rise in keeping a covered tank as small as 10g as well as a 150W MH. Your water is going to get HOT. Forget about jumpers, you'll be boiling your inhabitants alive
