i had 75 in a 90, and they ate the tips and stunned the growth
i had about 5 in a 90 they still ate it but it grew too fast, alot of the tips were chewed tho
my amanos must be well trained. I have several algae eaters in the tank including SAE's and nerite snails. I just inspected the UG and none of it shows signs of being chewed at all.