Hello; I had under gravel filters (UGF) in use in all my tanks from around1959 to near the end of the 1970's. For the first ten or fifteen years theywere the main filtration and they did an acceptable job. They did not remove detritusfrom the tank and I tried most of the various types of external filters Icould find and afford. I still have a few functioning air bubble poweredsurvivors and the remains of several early types of broken power filters. I ranthe UGF in conjunction with all sorts of external filters with good results.
Unlike all the power filters I have used the UGF never failed (I am notcounting the many air pumps that failed.)and I had very few issues or problemswith them. The power filters that I have running now have not failed as yet,but they will. (The power filters need a lot of attention.) The UGF bubbledischarge tubes would need a brush cleaning from time to time to remove thebuildup of algae from the inside. The air supply tubes and valves had to besorted and adjusted, but not very often. The UGF were set in place in a newtank setup, covered with gravel and forgotten about. They did not work wellwith fine materials like sand, so I always used gravel with them.
I broke down a lot of tanks with UGF over the decades. There was rarely much,if any, buildup under the filter plate. I have read comments about the UGFbeing hard to maintain. This makes no sense to me as there is no maintenanceinvolved. I have most always kept planted tanks and would find that the roothairs had made their way into the filter cavity of the UGF. The roots andplants were healthy and grew out well.
I have at least one survivor in a box and it will work fine if I ever decideto put it in a new setup just as it did when new. The ones that did not survivegot broken from my handling and the plastic simply getting too old and brittle.
I have been reading these forums for over a year now and have picked up alot of good information. Some of the currently pushed practices do not jivewith my experience. I have been trying to reconcile my fifty plus years of fishkeeping experience with some of these notions. The good thing is that each ofus can run our tanks as we see fit. I am fortunate to have a long background inthe hobby and know a lot of what works. I do sometimes feel sympathy for those forummembers new to the hobby that get hammered by the only do it my way crowd. Thereare usually many ways to run tanks that work.
UGF will work in a tank especially if you run some sort of external filteralong with it and it will be working when the other filters are giving youproblems.
I also do not use chemicals to condition my tank water or to set up a new tank.Been doing that for decades, but that may be for another thread.
If it makes any difference, and it should not, I havea couple of degrees in Biology and taught the stuff for over thirty years.