"I never drink water. Fish pee in it."
From the perspective of a zookeeper, especially one who mostly takes care of mammals and birds, with a smattering of herps thrown in, the world of an aquarist is just weird. For one thing, your day is confined, largely, to a single building, indoors all day long, whereas we trek back and forth across acres and acres of zoo. There is less focus on managing individuals animals, more on managing tanks and schools. Outside of marine mammals, there is less focus on training and behavioral enrichment, though there have been changes on this frontier also. Feeding aquarium fish is much different than feeding most zoo animals. (There are exceptions to all of these).
And then, of course, there is the major difference. There is no poop to scoop.
Fish do poop, of course. So do aquatic invertebrates. It's just that their excretory byproducts tend to vanish into the water that surrounds them. That, of course, is the same water that they spend their entire lives immersed in, breathing and swimming. Just because we can't readily see or smell the droppings doesn't mean they aren't there. And it doesn't mean they aren't a problem.
Plenty of aquatic zoo animals love to defecate in their pools. Hippos, tapirs, and capybara are notorious for it, but so do penguins, flamingos, and crocodilians, to name a few. The difference between these guys and fish is that they can survive on land - you can empty the pool, drain it, bleach it, scrub it, or power-wash it before refilling it. With fish, that's not much of an option - not unless you move them to an entirely different tank while you clean and reset their old one with clean water.
There are two methods that aquarists can use to keep the water clean for their fish. One is a partial water change - remove a certain amount of the water (20%, 50%) with a siphon and hose and replace it with clean water. The siphon vacuums among the substrate of the exhibit, sucking up not only water but uneaten food and droppings which collect at the bottom. The idea is that nastiness (that's a scientific term right there) gets collected before it accumulates. The second option is some sort of filter - chemical or mechanical - that removes or purifies contaminants in the water. Protein skimmers agitate the water and, well, skim off the bad stuff that floats to the top. Often all of these options are used together.
With the earliest aquariums, the dream was to create perfect, self-contained ecosystems of plants and animals, whereby the plants would purify the water and the animals would support the plants. Unfortunately, it didn't work out too well in long-term studies. The idea has gotten some new attention, however, with an increased focus on biological purifiers. For example, mollusks like oysters and mussels naturally filter water as they feed. Perhaps aquariums could someday culture colonies of shellfish to purify at least some of their exhibit water. Not only would it help clean tanks in an environmentally friendly manner, it would serve as an educational demonstration to visitors on the importance of oysters and their relatives in maintaining healthy aquatic ecosystems.
That, in the end, is why I think I'll stick to my land animals, my rake and shovel. The job may be harder and more physical and certainly smellier, but it's also a whole lot simpler.