All sizes of tank need about the same frequency of water change. On my 55 I try to do about 15 gallons once a week. For me that is 3 buckets full since I use a 5 gallon bucket. I mix the dechlorinator in the bucket while the bucket is filling then use my gravel vac to drain the bucket into the tank. Pouring the bucket into the tank just stirs the substrate too much and moves all the decorations around. I pull the hood off the tank and lay a board across the top of the frame to give me a place to put the bucket while it drains into the tank.

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Fishless cycling