Contemplating a new tank that would be 48x48x36" Can tall tank owners tell me about maintenance issues. Local guys are telling me to stay away unless its fish only
Anything deeper than your arm is a horrible idea. You will get tired of having your shirt sleeve wet and will eventually stop doing things on the bottom of the tank and regret buying a deep tank.
Even with something only 24 inches tall, you can have problems depending on how long your arms are. I'm on the smaller side, and I struggle to reach the sand bed in my 24" tank, even standing on a step ladder. And then, of course, I run into the light fixture, and it's generally a pain. If I could do it over again, I'd probably have made the tank 22" instead of 24".
There are of course grabbers and such that you can get to extend your reach, but they're never as precise as your actual hand is, and you'll struggle to maneuver precisely with them. At 36" tall, you'll really struggle to get anything down near the sandbed, which doesn't seem like it'll matter until you remember that corals can come dislodged, that you might need to reposition things...
Basically, unless your tank is large enough that you can physically get into the tank yourself to service it, don't get deeper than you can reach with your arm, at the top of the tank, past any eurobracing (and a tank that tall is likely to be braced, so remember to account for that when measuring your access). And a 48 x 48 tank isn't nearly large enough to allow for a human-sized animal to get inside of it for regular maintenance.