thanks a lot will consider buying one thwn instead of making one at homeJust buy one unless you already have all the materials to make them I guess. They are very cheap though. ATI Hydro-Sponge can be had for less than $10 for that size of a tank. Most likely you would save money just buying it, but if you want to DIY because it's fun for you, They are not overly hard to make. Basically you just need a way to move water through a sponge and back out the other side. It can be done with an air pump powered sponge or a powerhead would work too. There are a bunch of videos and tutorials on the web that can give a better step by step than I can provide.