i also use fishtanks for my t's but i go to pg glasor glasvriend give them the measurement of the tank and they cut me a covering lid of glass ofcourse usually a small bit bigger than the tank itself and about 1cm thick so its nice and heavy but not to heavy ofcourse,they also drill a few holes about 6 in the lid for ventilation and polishes the edges so that it is nice and smooth,at home i then take 3 skaniere haha sorry for the afrikaans not sure about the english wording this early in the morning and take silicone to stick it to the glass its really easy to do and it works beautifully no escape thus far with my t's that i keep inside the tanks they are about 11-13cm in size...keep well