how often do you change water for the tropical fish?

It depends on which tank, as my largest tank is now getting done every three weeks like the ponds. The Catfish every week and they are making a big mess. My Endler's are on an every other week schedule. Keep in mind I have a large canister filter on every tank and corner filters. I have 30 tanks and sell fish. I rarely have sick fish, but do have a hospital tank. Its never had an Endler in it, but the Catfish have been a nightmare to keep healthy. They don't like my water and refuse to let their food stay on the ground.

Once a week is probably about right but it depends on the size of the tank and the number of fish. I have a filter system on my tank and I changed the filter quite often rather than the water. I also have to add treated water as it evaporates quite a bit. You didn't say whether you had the filter, you had algi eaters, or the size of tank and number of fish. You sound very dedicated about the care I must say though.

I have 10 aquariums that have filters on them and I change at least 20% of the water each week. My fish love it because they are always breeding for me. I have not had any diseases in my tanks for many years. Yes you need to cycle the tank where bacteria will break down the ammonia given off by fish into nitrite and another bacteria will break down the nitrite into nitrate, The bacteria live on solid surfaces ., not in the water (except when they are blooming in the beginning). It is safe and actually good to do partial water changes frequently, some discus breeders will change 100% of the water each day.

It really depends on what species we are dealing with here and their appetites. Some fish need frequent yet not stressful changes. Tropical fish love mature water, that means water that has been sitting for a while with vegetation. Example if you have south american fish its better not to change the water frequently because they are a bit used to acidic water. Plant living aquatic plants in their tank it helps reduce bad chemicals in the water. Filters are a must to maintain water clarity and prevent uneaten foods from polluting water. Use this water change system, take out 1/4 of the water each week and add 1/4 fresh...and complete change and filter cleaning once a month. Don't change too often your fish will get stressed and you will start wondering why they are always hiding and they begin to get health problems.