ImACoolguy
Aquarium Advice Addict
Not only stressful to the fish. I believe it would be stressful to the BB also. The new water unless pretreated will have an effect on your BB. I usually do 30-50% every Sunday. Rinse filter in tank water every 2 months that's where most of the BB is living. Never vacuum much gravel area unless there happens to be lots of debris or algae. The gravel also house a good supply of BB.
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I'm a personal believer there's hardly any living in the substrate. In the case of freshwater of course. IMO 99% lives in the filter. I've completely changed substrates in a 45g and no mini cycles or parameter disfunction. There's a tad on the substrate and decor but not enough to make any significant difference.
Caleb