I have a 35G pond liner made of heavy duty plastic that I keep in the duck pen for the ducks. It has no drain/outlet, and no pump, and after about 24 hours the water is sour and the ducks can't swim or drink in it. I have to drain it and dump it out (not an easy task) and then re-fill it with fresh water. These ducks will not be with me much longer, so I'm looking for a cheap solution to the stagnant water problem. I have a few small aquarium pumps that are capable of pushing water a few feet, and I'm thinking of installing one in the bottom of the pond with an outlet that rises above the water, just to move/stir the water around and aerate. Will a small amount of agitation and aeration be enough to keep the water fresh, or is there no way to battle the stagnant water in the summertime heat?