Yes, otocinclus produce a lot of waste. They constantly graze on algae around the tank, so even though otocinclus can help you control the tank’s algae growth, they are also constantly producing their own waste.
In order to deal with the waste produced by your otocinclus, you should perform weekly 25-30% water changes and monthly tank cleanings to keep the aquarium clean.
With that said, otocinclus still produce far less waste than other algae-eating fish, such as plecos.
Additionally, the waste otocinclus produce has very low ammonia content due to their herbivorous diet, so even though their waste may make the tank appear messy, otocinclus don’t contribute a lot to the bio-load of the tank.