The last phase of the nitrgen cycle of turning no3 into N gas is limited only by surface area, IME. In a tank with real functioning live rock (not dead/dry that is filled with organics and even terrestrial phosphate which does not allow anoxic bacteria to colonize), I have not met a bio load yet that could not get kept down naturally. Bare Bottom tanks already have limited surface area. I once had a 300ish G with about 30 fish in it - mostly larger tangs that ate coral (yes, tangs often eat coral as they get large), triggers, gunea fowl puffer and two basketball sized lions. I fed this tank so that they all fish grew and were not aggressive - kilos of raw food a week and a 5lb pail of pellets every month. This tank had no3 under 1 because of the few inches of sand and live rock. Phosphate was another thing and it climbed and climbed and the rock and sand got SO saturated - eventually all of the macro died and even the coralline... I was probably above 2.0, but just guessing. I bought a 55 gallon drum of the aluminum oxide that was used in bulk to dry air (or something like that?) and changed it out every day or two for about 5-6 months and about 30 gallons of media later was down under .1 and the coralline started to thrive again. I still use that rock today that was once SO loaded with P and now has a very low concentration - some of it was from the GBR back when you could get rock from there and some from Marshall Islands which was the best rock ever imported.