One more thought... I'd do nitrate testing throughout too. I don't know your current water change regime but you will undoubtedly find more nitrate with more fish and so you may need to do larger water changes more frequently. That said if you are already on 50% weekly then you're in a good space anyways!! Fortunately 55litres is not too hard to do a big water change on! My nano tank and big tank both take a lot lot longer to sort out than my 64 litre!
Great, thanks for the advice here and above. I’m have been doing three water changes of around 50% per week. I might drop this to 3 at 39% or two at 50%, just because I have read that the shrimp don’t like instability in the water parameters. What do you have in your 64 litre out of interest?