How normal is it to lose a fish?

[Sk8r]

Answer: it is not normal. I expect fish I get to live for many years unless I make a few basic mistakes.
1) mismatched occupants of tank: getting a predator, or two that don't get along. You avoid this---by asking about combinations.
2) I don't impulse-buy unless I KNOW the species well.
3) I don't push the limits of my tank. I leave 'chemical' leeway for accidents, pump stoppage, etc, just as I leave a physical safety space in my sump for a power-off condition to drain water down. Leeway, leeway, leeway. It means, in its disaster application, the space a sailing ship has between it and the rocks on the lee side, the direction the wind is pushing it. You always need leeway in a system.
4) I have a float switch that keeps salinity in my tank absolutely spot-on.
5) I don't overfeed. And I have a fuge crawling (literally) with life that will take anything that escapes the dt.
6) I watch my corals. A few touchy corals are a good thing in a tank, because they warn you if ANYTHING is slightly iffy about the water. If the corals ain't happy at 7am, give it 8 hours and the fish ain't gonna be happy either. The tougher [lps, button polyp softies] corals are sincere mine canaries. They don't die: they just tuck up and wait for better conditions; and if your corals are tucked, you've got a problem that needs urgent attention. Your fish will tough it out as long as they can and THEN they'll start acting 'off'. I honestly respect FOWLR keepers: they have a much harder job detecting a problem.

If you have had a member of a species die---find out why and fix the problem before you replace it.

And if anybody tells you anything is 'rare'---absolutely avoid it until you have a year or so of experience. "Rare" means either "they almost NEVER live" or "expert-only." If you spot any breathtakingly beautiful fish you've never seen before---I can assure you there'll be another. DON'T buy a fish that's out of the ordinary. Read: "rare." There's a reason.

And ---Quarantine, quarantine, quarantine. If it's going to break out in purple spots, best it do it in qt, NOT in your nice new tank where it can shed nastiness over all the cool stuff.

[disc1]

All great advise, but sometimes they just die. Sometimes they weren't healthy when you bought em and there was no way to tell until they croaked. Sometimes they just don't like living in a glass cage and give up the ghost. Sometimes there is no explanation other than that the Good Lord called em home.

[ryeguyy84]

what about fish that disappears? I had a dottyback that went completely missing. came back from an over night trip and it was gone. is that common?

[Sk8r]

THere is always a reason.
a) sometimes they came in sick. If you took the advice about quarantine, you only lost one fish, not all of them. This also goes for corals, but you dip them.
b) sometimes you make a mistake: acclimation kills a lot of fish. Read the sticky.
c) sometimes you get fish from a dodgey source: it's a case of 'know your source' --- and if you have an apparently healthy fish that dies a week in---and it's not disease, you may have a fish that was collected by using cyanide [no kidding, it is done by unscrupulous collectors] or dynamite. This is the fish that nothing can save. They will die of organ failure. There IS always a specific cause. And if you suspect it, do not buy from that source again, and if it came from a store, TELL them. They may have a new distributor they need to look at critically.
d) we do not know the age of these wild-caught fish, and sometimes a fish at its max size or a little over it is also at its max age. Many marine fish live for over 20 years. But in the case of, say, a 5" yellow watchman, when 4 1/2 is the given max---that fish may be pretty old, and it's a wonder he's made it through the distribution system alive.

Re a disappearance: you may find some species can disappear for several months---and pop up again---in your sump, or denning on the back side of your rockwork (try a mirror), or in the overflow box. I have a redstripe highfin goby living in my sump/fuge at the moment: he'd disappeared for about 2 months. I won't even bother catching him until he gets big enough he can't go through the overflow teeth. The trip down is a rough one [basement sump.] There are also carpet surfers: fish that jump to escape a moment of panic, and miss the tank altogether: these sad wisps usually end up on the carpet behind the tank. You can prevent this by jump shields.

You will also find predation happens. And sometimes from the absolutely most crazy source---I had a series of fish deaths I couldn't account for. Always at night. Well, the fish I favor (blennies and gobies) are bottom-sitters when they sleep. And the elephant-ear fuzzy mushroom has hair-trigger reflexes, and gets quite large. My beautiful fuzzy mushroom was suffocating my fish at night: they'd sit on it, and fast as you'd ever believe, they were bagged and suffocated.

And if you have a lot of clean-up crew---any demised fish will be gone in 24 hours, even if fairly large.

[Jlobo]

What exactly is a float switch Sk8r?

[Sk8r]

You know the ball float in your toilet tank? Something like that can operate an electrical switch off-on as well as, say, just open a valve. An ATO (auto-topoff) uses a little float switch, some about thumb-sized and contained in a tube, to close a circuit, turn on a pump, and deliver fresh ro/di from a bucket. This is the best sanity-saving device in the hobby.