Originally Posted by willieturnip
Your slacking, I can think of a one at least.
Any tank that needed to be quiet I suppose, which would be fine so long as water changes are big and frequent. Which is why smaller is better in this scenario.
I just want to clear up that Water Changes and Protein Skimmers do not do the same thing. In fact, I use the two for very different reasons altogether.
I use my Protein Skimmer to remove dissolved organic compounds from the water column. This cannot truly be acheived at the same level by water changes. The skimmer is working 24 hours a day and hopefully having all the water in the tank run through it. Even a large Water Change of 30% would only remove 30% of the pollutants (Which I don't reccommend; large water changes can shock the inhabitants of the tank, at the very least stress them out). The only thing that I would substitute for a Protein Skimmer on a small tank would be a bag of activated carbon (I use both on my 150).
I use Water Changes to replace trace minerals and keep my water at desirable Cal and Alk levels. I have found that changing 10% of the water a week (along with dosing) helps keep my Calcium between 400-450 ppm, and my Alkalinity between 8-12 dKH. I don't even consider the water changes as a way to remove pollutants, as my Nitrates are almost never detectable, and 'Trites and Ammonia are always zero (as a result of Live Rock and Live Sand Bed).