I have a 240gal planted tank full with rummy nose tetras, angels, and hatchet fish and a fishroom with 6 20gal tanks running with endlers, shrimp and some orange line acaras . I do 50% weekly water changes on everything. I siphon (python no spill clean and fill hose system) the water into my gardens, dirty fish water does wonders for plants. I then add enough dechlorinator to treat total tank volume and connect another hose to my sink and refill. I use a little hot water if the tap is too cold, using my hand as a rough guide. I don't like using test kits and have not used one since my tank cycled 2 years ago so i just keep up on water changes. If you dose fertilizer, that is another reason for water changes. I used to do EI dosing which required 50% wc weekly. Had the habit ever sense.