Zimmanski
Aquarium Advice Addict
Your parameters suggest an uncycled tank, or that the BB is adjusting to your additions, OR that pleco is already producing enough bioload that your biofilter can't keep up. I would seriously consider rehoming/returning the pleco, I'm not educated enough to say if any pleco can be in a 16gallon tank but I do know the amount of bioload they produce would seriously limit what other fish you could put in the 60L tank. For example I really wanted a gold nugget pleco for my 55 but after I found out that they produce so much waste and that even one would lessen the amount of fish I could put in the 55g, I decided against getting one at all.