Somebody here mentioned closed tops are a no no because of the light they cut down but I strongly disagree. Sure, you have to clean them every 2-3 days, but they not only keep heat in (I use a 50w heater on a 40gallon tank, all because its sealed!), but you also cut down on water evaporation A TON.
BTW they dont have to be SEALED, as that would cause insane amounts of condensation. But do have them "tight-ish" fitting with a little space around the edges for small amount of air to circulate and keep condensation to a min.
Also, keep your tanks at 78 degrees, nothing higher.