Lets talk about undergravel filters, no really. Old technology? Maybe, but so is running water. When we got tired of going outside to pump water, we didn’t stop using water, we invented faucets. OK not a great analogy. In the beginning of the aquarium hobby, which was right after WW2, we all kept goldfish and guppies. The first thing we did was to put in an undergravel filter, why? Because it worked. Originally we thought it was a mechanical filter and we loved mechanical filters because we liked to filter out particles. Water quality didn’t matter as long as we could see the fish. Clear water was also essential to locate the dead fish, and we found a lot of dead fish. Not because of the UG filter, but because we were using it wrong. We read the instructions and that was our first mistake. The people who invented and sold UG filters were not at fault, they also liked to filter things and an UG filter does that fairly well. Unfortunately, for some reason we didn’t want to think of all that stuff that was filtered but still in the tank. We must have been busy watching those Ann Margaret movies. But in our defense, freshwater systems do great with UG filters. I am not sure why but they do. Then we all got high class and changed most of our systems to salt water. We loved our UG filters so we kept them, after all, they worked great and “filtered” out all that “stuff” that we figured we needed to filter. Then there was Bonanza on TV and we again forgot that an UG filter does not remove anything. Boy were we stupid. That’s when 99% of us removed the UG filter. But there is something I like to call those people, and that is “wrong”. The UG filter is fine, we were the problem. It is not a “filter” even though that is what it reads on the box, it is a water treatment system. If we use it as a filter, our tanks will crash, guaranteed. Robert Straughn (The Father of Salt Water Fish Keeping) advocated UG filters as the greatest invention since tap water. The man was a genius but he didn’t know the reason the UG worked. The UG “System” will only work if we keep out the particles or as we like to call it “detritus” (dirt, crud, shmutz etc.) The gravel on the bottom of a tank vastly increases the real estate that bacteria can live on. Bacteria are like us, they like water front houses with continous fresh calm breezes and lots of easy to get food. Gravel is perfect for them and, like apartment buildings, they can live on top of each other without getting in each other’s way. Water with no particles flow past those bacteria, the bacteria process out what they want, which depending on the type of bacteria that could be nitrate, nitrite, ammonia or Harvey’s Brystal Cream. Too many particles and the bacteria will think they are living in a slum and the water flow along with their oxygen and food will stop. Some bacteria are lucky and they like it when there is less oxygen, they have larger noses to collect oxygen, maybe not, I don’t know, but they process nitrate in the absence of oxygen. So some detritus in the gravel will limit oxygen and actually help those bacteria convert nitrate and detritus is going to get in there no matter what we do. The best way to run a system like this is to take the UG filter and throw out the instructions. Then build a manifold above the water. Connect the tubes from the UG filter to the manifold and pump water into the manifold so all the tubes get a slow even flow. The water going into this manifold should first be strained to keep out those large schmutz particles. Run this arrangement slow. The slower, the better. Will this run for fifty years with no maintenance? Absolutely not. A few times a year you need to stick a canister filter of some type in there and stir up the gravel. It helps if most of the rock is not laying on the bottom. That doesn’t look good anyway so figure out how to do a dynamite aquascape job. It may get you a girlfriend, maybe not.