It amazes me how nervous people get about their filters during a water change. Where did the bacteria in your tank come from in the first place in most cases? The tap! The starter colony of bacteria came in amongst chloramine/chlorine laiden water, and are a chloramine/chlorine resistant strain in the first place in most instances. Unless you have ran the tank for many years without ever doing water changes adding back water without
any chloramine/chlorine in it (un-likely in most cases), and some how got non-chloramine/chlorine resistant bacteria from somewhere, a chlorine/chloramine resisant strain of bacteria will be living in your filter
I'm not advocating that new fish-keepers go out and stop using dechlorinator at water changes (though I don't use the stuff anymore), but I whould point out that in most cases, doing a water change without using dechlorinator will do no harm t the filter, unless the water board has recently switched which chemical they use for water treatment, or it is a very large water change you are doing
API Stress Coat is an OK water conditioner for most community tropicals, but if you get into stuff like Puffers, Discus, loaches and other fish that are sencitive to stuff in the water, it
can cause issues. The last few times I used Stress Coat with Discus, they went jet black, became smothered in excess slime and started flicking and rubbing aganst objects. I realised I'd used the wrong conditioner and did another large water change, quickly solving that issue

Stress Coat contains Aloe Vera to "enhance the slime coat" on fish. The only obvious way for it to do this is to irritate the fish, causing them to produce more slime as a responce to the stress of being irritated. There are many reports on-line of Aloe Vera being an irrtant to fish, and when I ask the API rep at work, he always dodges the question and attempts to change the subject quickly.
When I used to use dechlorinator, I used API Water Conditioner. It's more concertrated and a couple of quid cheaper, and also does not have the problematic Aloe Vera in it
All the best
Rabbut