Please Help With My Fish Tank Community Question

Very sorry too, to read about the fish. I did think he looked rather weak in the hospital tank. Even if there had been a suitable medication, it seems he wouldn't have had the strength to tolerate it.

Several years ago I had a betta that was swollen like that. In the end he was so bad I put him down. I examined the body and found the abdomen was full of yellow goo 

UV lights are not a cure-all. They rely on water born bugs flowing past the UV light before they can infect a fish.

That doesn't sound pleasant at all... Least of all for the poor fish!

Are UV Sterilisers supposed to give off visible light ie. like a blacklight gives off a violet hue? My tank came with a UV steriliser unit on the rear and I've never noticed light coming from it but never looked closely....

Interesting... I wonder if mine is working or not, I just assume since all seems well that it is... But if it weren't working how would I know?

In that case, I'd say it's definitely no longer effective. The previous owner of the tank was my mates' daughter. He ended up doing all of the maintenance towards the end of them having fish in it as she would let it go to the point where the spray bar flow would stop because of the gunk build up (nice) and to be quite frank the filter tubes were disgusting when I first got it. After me owning and running it for 3 months they are close to being completely clear...

Suffice to say I highly suspect the UV filter will have the original bulb inside it. I may replace it at a later date. Everything is fine in the tank so no need to do anything with it.