When you have a tank that big (like 50+ gallons), how often do you need to generally do a complete water replacement/cleaning? I know once you get to that size there are some fairly advanced filtration systems and such, but how much do you need to do the entire thing?
Never. Doing that kind of "total cleaning" would just kill/weaken your beneficial bacteria colony (which is what processes the ammonia generated from decaying waste and keeps your water in good condition).
I have a 75 gallon tank that's pretty heavily planted. I run two Fluval Fx4 filters (this is probably overkill, but the tank is stocked pretty heavily with big fish and I like the extra flow. They're great filters).
My normal maintenance routine....which I try to do every week but sometimes push it out to 10 days or even 2 weeks if I get lazy (again....the extra filtration and plants allow me to get away with this. It really just means extra algae on the glass, not a dip in water quality).
- Trim all the dead leaves off the plants.
-scrape all the algae off the glass (combination of toothbrush/sponge for the softer brown algae a razor blade for the green dot stuff that's a little harder)
- Change ~25% of the water with a python hooked right up the sink, disturbing the plants or substrate a little bit to knock some detritus loose if I see it.
The normal routine takes ~30 minutes, most of which I can spend just sitting on the couch watching TV while the water goes in/out.
Other than that....every couple of months I'll use a different gravel vac (which I take the head off and just use the hose, which gives more pinpoint suction) to thin out the snail colony that's growing in the tank. They just get kinda unsightly every once in a while.
And then about every 6 months (on a rotation, so I dont do both at the same time) I pop open the filters and clean them out (using tank water so I dont kill the bacteria colony). Should probably do this more like every 4 months, but its a decently long job.
My tank isn't really pristine (I have various types of algae growth) but its cleaner than 95% of tanks I've seen and it keeps it in presentable condition for my living room (if I have to see it every day, I want it to be clean). Fish are healthy and the plant growth is ok (not great...working on that).
I've been kicking around the idea of getting a much larger tank for my office/finished basement (like a 240 gallon 8 footer with a sump) for years....but the logistics of cleaning it concern me. I'd have to put in a sink downstairs and find a way to heat the basement better (it gets really cold down here during the dead of winter). Heating a 240 gallon tank (probably closer to a 300 gallon system with a sump) to 80 degrees in a basement that probably gets down into the low 50's at night just seems like a bridge too far.