Sorry if I caused you more stress was just offering some options
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I agree that you don't want to make any drastic changes to lower pH. Sometimes trying to fix something can cause more problems. IMO adding a 2 liter of DIY co2 is not a drastic attempt to lower the pH. It is fun to do, benefits plants, reduces algae, and naturally lowers the pH by a very small degree if at all in a 55g.
It's true fish can adapt to different water parameters. Personally I prefer to try and keep fish in an environment close to what they came from. I would not keep rummies or GBRs at a pH of 8, but if it works it works I guess.