Hi all, I got rid of my fishes (donated to one pet shop) in the last summer, trying now to get rid of my tank (100L). From my experience, trying to create a balance in the microsystem of the aquarium is the key of a successful aquarium. Best not to clean the filter, at least not all of it, try to use ceramic filter, which it should be the host of bacterias which are decomposing nitrites (or nitrates, I always mess them up :rolleyes:). I modified the stock sponge filter by cutting half of it away, and replacing with ceramic cylinders, and cleaning now and then (i think it was once per month, or even rarer...) the sponge filter, and maybe once per year the ceramic cylinders. Then repopulating with fresh bacteria culture (sera bio nitrivec) and, of course, sera aquatan, including the times when I was partially changing the water, with the amount of water changed (usually it was 20-30L - 20L out, and refilling the rest up to the top minus 5cm - a lot of evaporation though). I had also some problems with the algae, of course, but that was due to the fact that I was using the built-in light too many hours, as soon as I stopped using the lamp, the problem solved by itself. A good advise is also to get some algae-eater fish, as the ones suggested here (usually they go along very well in the community tanks) http://aquariumalgaeeaters.blogspot.com/ (beware of black mollies, as they are viviparous fishes, as the guppies). As Diane suggested, the placing of the tank is very important, as it shouldn't get direct sunlight at all, but it needs indirect light to be ok. Regarding the Squarepants' tank, I would suggest getting rid of any of the two species, as the goldfish prefers cold water, and guppies a tropical climate. Putting them together is like trying to raise a snow leopard with lions.... Beside this, the temperament of golden fish makes him a lone or pair only fishes in aquarium, as they need a lot of volume of water for one fish. Generally speaking, a method of calculation of the maximum number of fishes/aquarium is 5 cm of fish (at maturity, be warned!!! they will grow :tongue:) per 10 L of water, as general guidelines for tropical fish. The temperature should be set accordingly to the type of fishes in the tank, so when you buy a fish, don't just go and tell to the guy at the pet shop "I want this one because I like the colours", ask that person on which climate he should be kept, and if it fits in yours at home, buy it, if not, you'll kill him soon, or you'lll get a discoloured and ill fish. Unfortunately, my experience is limited just to the tropical fishes excluding cyclids (I didn't like the idea of having a war in the tank, as most cyclids tend to have its own territory). If any other advice is needed, I will gladly share whatever I can help with.