Mouth fungus is not an unusual (bacterial) disease, though it's not often a problem in an established tank. But as soon as you buy a new fish, you run the risk of new diseases coming along with it, some of which will not be apparent at the time. Consider that an LFS will buy a hundred fish a week - plonk them in their own tanks, and then run the whole lot on a central filter system. If so much as one of those fish has a problem, there is a chance that that problem will spread to all the other tanks too. Often the LFS will start selling the fish on before they themselves are even aware of it.
Recently I bought 3 Plattys and put them in the new guppy tank. A week later, one of them was showing signs of fungus on its head which seemed to be getting worse. So I put some meds in the tank. Didn't see the Platty for 2 weeks after that - whereupon this skeleton came dancing out on its tail. (I knew the fish must have died - but I couldn’t find it no matter how hard I looked). All the way through that, the water tested fine for everything, no other fish were affected in any way - another it time may have turned out very differently indeed. Maybe the med dose helped to control it - no real way of telling.
My point is that the treatment of sick fish is always a game of chance. Identifying the disease is the first problem, correct treatment the next. Then you have to worry about the other fish going down with it - often secondary infections appear. One simple white spot on one fish and we're biting our nails for weeks.
The best thing to do (in my opinion) is to observe a few simple basic rules of thumb. If the fish is still sick after two days - then treat the whole tank with a combination anti-bacterial/anti-fungal med. This will work in 99% of cases. Even if you have a fish that gets sick and dies the same day, and none of the others seem affected - still treat the tank. (Don’t forget that carbon must be removed from a filter when using meds)
If the fish is showing unusual symptoms - eg not it's obviously fungus or whatever, then ask around, check the net, post some pics if you can. This doesn't happen often, but we do get the odd unknown problem, and people on here will help if they can.
Things you can't see in the tank - well, yes, there are a few.........water conditions are often a factor. Not just the Ammonia, Nitrite, and Nitrate levels - there are build ups of all sorts of things your test kit doesn't look for. But there are common threads even here. The key words are "build up". Uneaten food that you can't see gets into the gravel, dead fish you know are in there but never find (until they come dancing back out) may not give you an ammonia reading, but will give the nasty diseases plenty to feed on - rotting fish - lovely grub. And all the time this is going on, we're looking through the front of the tank - all is clean - the gravel is vacuumed regularly - and it makes no damned difference at all, because we miss the same things every time - that's how a build up happens.
Prevention is better than a cure - easy to say huh........still, we have to try. Regular water changes are the first line of defence. Whatever is going on in our tanks, it’s best kept diluted. Cleaning is the next one - and not just around the ornaments, but under them as well. Every now and then, take the tank apart - all of it - nothing but fish and water remains. I take my stuff out into the yard and blast it off with a hose. Even in what looks to be a squeaky clean tank, clouds of crud appear in the water during the process, as all the stuff that’s been hiding for ages gets to see the light of day - (and shortly afterwards, the inside of a filter). It takes the tank a day or so to settle down again - but it’s worth the effort.
When you’re buying fish at the LFS - look at all the fish they have for sale - not just the ones you’re interested in. If you see so much as one sick fish, there is a good chance that illness will be in all their tanks - one guppy in a bag is all it takes to wipe out everything you have once you get it home. Be cautious - be fussy - this applies as much to where you shop as to the individual fish you buy.
And when you apply all of the above - and you still run into trouble......then welcome to the wonderful world of fish-keeping. None of us are perfect - and no-one can beat Mother nature at her own game every time.
Welcome to the tank.........
