Tank tear downs

[Blacklight]

Back in the day when I used to run my old aquarium, tank tear downs every few weeks were the rule of thumb. (Remove all the fish, remove the gravel and clean it, clean the decorations, etc...)

From what I'm reading now, this seems to be no longer the case and you're supposed to do 20% water changes (while vacuming the gravel with a gravel siphon). Is this true, or are monthly tank tear down and cleanings still recommended?

[Gryphon]

I think it all depends on if your tank is cycled or not. If you completely tear down a cycled tank, you kill off your beneficial bacteria and have to start the process over again.

The size of the tank is also a big factor. Tanks under ~2g are usually recommended a 50% water change and a 100% water change once a week, while larger tanks do ~25% to 50% once a week, and 100% a month.

I think it also depends on what levels are in your water and individual fish keeper preference. I have planted tanks, so I never tear down mine.

[Blacklight]

So when I do my 90-100% monthly water change, I should just pretty much do a vacuum of the gravel with the gravel siphon and leave it and not do the old "put the gravel in a pan and scrub it under hot water till no more crap comes out of it"?

My tank isn't a planted tank. My wife prefers the silk plants.

Also, when doing a 20% water change. I've seen people leave the fish in the tank for this. How do you add the new water to the tank without shocking the fish with the temperature change? I know this is a stupid question, but I've never done a water change with the fish in the tank before. I assume you just have the water at room temperature and treated with the water treatment drops and you pour very very slowly? I would rather make %100 sure I'm doing this right as back when I was doing aquariums, the 100% teardown/sanitize was the way to do things. Not doing that is kind of a new thing for me.

I know enough not to change the filter at the same time as a water change.

[Hallyx]

The monthly teardown and the weekly 100% water change with gravel washing and all was to prevent the nitrogen cycle from forming. Before the days of effective water conditioners with their ammonia control feature, and filter media capable of harboring bacteria colonies, this was a way to prevent ammonia spikes which are dangerous to livestock.

These days, the cycled tank is the preferred habitat. The bacteria grown during the nitrogen cycle convert the ammonia (eventually) to relatively innocuous nitrate which is controlled by weekly 50% (approx) water changes and/or by plants.

Even small (2.5g) tanks can be cycled and this is much better for the stock.

Cycling is not for the convenience of the keeper, but for the health and safety of the fish.

[Hallyx]

Leaving the fish in the tank is customary for all water changes these days. They get used to the siphon, so little stress is involved.
Some fish enjoy playing in the refill stream.

Most keepers adjust their refill water at the tap using a thermometer to match the tankwater temperature. Some claim to be sensitive enough to do this by feel. I use a thermometer to keep the refill water within +/- 2.0* of the tank.