[demonsquirt]

Cant be any mixed feeling. In a SW tank placing any cover will hinder amount of dissolved oxygen in the water.Also your waters PH will suffer and this will also increase water temp.

Firstly, water movement will overcome the problem of thermal layering by mixing the warm and cold water layers, so we end up with an evenly heated tank.

The movement of water in the tank also prevents the formation of a film on the water surface, which would inhibit gaseous exchange between the water and the air.

Water moving around the tank effectively increases the surface area of the tank by constantly changing the layer of water in contact with the atmosphere. This, of course, dramatically increases the rate at which oxygen can be dissolved into the water and carbon dioxide released into the air. Well oxygenated water is essential for the health of the fishes, plus, we can keep more fishes in a given space if the water is well oxygenated.

Moving water carries oxygen to the nitrifying bacteria in the tank, which are responsible for the breakdown of harmful waste products, and also carries nutrients to the plants.

A strong movement of water in the aquarium, as produced by a power filter, provides the fishes with a current in which to swim, and many fishes find this both enjoyable and beneficial.

As you can see then, water movement in the aquarium can be tailored to suit the type of environment we wish to establish.