Is that true?

I think the whole point was to balance out selling just enough fish to make a small profit and to only put the bare minimum into maintaining it. As someone else commented before, putting too much effort to maximize food and chemicals actually hurts your ratios. I only put a couple dollars in at a time for when I actually need it. The minimalist approach.
Just buy every upgrade and keep around 90 fish total (young and adult) in the aquarium, only give the necessary ammount of food and cleaning (until the words turn green in color).
It's basically self sustainable and gives you around 2 to 4 $ every time you manage it. It's free money all in all, but you don't have any way to actually use it after buying all the presents, don't know if DPC plans on adding ways of expending money apart from buying from Jacob and the cheats.
You can waste your excess money on the manatee, but that would make it impossible or very difficult to upgrade the tank fully.