+1Make a fish room in the basement with all three! Then you"ll go down their and have your own space.lol .
I was a code enforcement officer for all systems up to three story building. 16inch on center floor joist means very little until we know the dimensions of the joint ie 2x6, 2x8 etc. Then I would have to know the span. The length of the joists until there is another support. Then I would need to know the thickness of the floor plywood and weather it is two apposing layers or one with your flooring over it. You see code is the minimum to hold a normal static load and this varies from state to state. Fish tanks are not static in an earthquake they are a live load. With this info I could give you a bit of advice. Without this info everyone would be guessing and taking on a liability. A 220 gallon tank swaying is a great deal more pressure on a structure then one would think. As it sits it would only be about 1lb per square inch of floor surface which does not seem like a lot. but when it starts moving all the weight shifts from one side to another increasing the weight to a live weight to over 7000 lbs on one end then the other and back etc. This is where structures run into problems. 3+ inch concrete is always better when over 150 gallons.
ya i almost wish the basement wasnt completly finished just for reason's like this as well as being able to get a slow drip system attached to it and add a drain off the tank for waterchanges lol .... ya im unsure of were the next support beam is from the outside wall here, i looked in the furnace/storage room to see if i could see a support beam on the side of the room cloest to the outside wall where my tanks are but cant see anything with all the heat/ac ducting everywhere, BUT i see one on the other side of the room but tht doesnt help me at all .... hahahaI’m not saying you can or can’t but I have a 265 on my main floor in the corner perpendicular to my joists and am fine with no sagging and a 125 right across from it on the same joists which are resting under a support beam. I think this is something a lot of people over think, but I know there are people out there that have had problems. I would think that as long as it is perpendicular and near an exterior wall you should be fine. I also have 2*8 joists in an unfinished basement so I can see how everything is laid out.