I just got a 29 gallon tall off craigslist with 2- 8 inch oscars, 1- 5 inch Jack Dempsy, and 1- 10 inch pleco. The water was actually thick. The guy was so proud of it. He said "yeah I only have to change the water every two weeks because I've got an undergravel filter". I was sick. These guys are bouncing back in my 90. But even then I am selling the pleco because it's still quite the bioload. Good deal tho- $ 50.00