Watch out- newbie who thinks she knows it all
While I agree that messing with the tank- no matter what you do- affects the ecosystem, some things are so small that the ecosystem will bounce back almost immediately, and some things are good for the ecosystem.
Most of the beneficial bacteria is in the filter media; a small amout resides in the water/gravel/decoration...etc. While doing a water change does take away some of the bacteria, the amount is so small that it won't matter and the beneficial bacteria in the filter media will (in an established tank) be more than enough to hold the cycle. Water changes also help to remove ammonia, nitrites, and nitrates; too many of these can be deadly to fish.
As for dechlorination, I disagree. Chlorine/chloramines can be deadly to fish. Back when I first started keeping aquariums, there were a couple times when I forgot to add a dechlorinator. I could definitely see a change in the fish- they were breathing rapidly, laying on the gravel, some getting stuck to the filter intake- and a couple even died. A dechlorinator is a must.
Threaded Mode