Sick Black Phantom

Hi all I haven't been on in quite a while as tank was going really well , however I've recently started to have some issues. It started a couple of weeks ago when one of my black phantom tetras suddenly lost half it's tail. This fish ever since I got it has had a strange lump either side of its tail but it had been fine in all other aspects prior to loosing it's tail. It's tail promptly started to grow back but about a week ago my serpae tetra started to swim vertically with nose pointing upwards.
I had to go out to work and I feared it was deteriorating so I swapped it over to my hospital tank, when I checked it half an hour later it was lay on the bottom but jumped up and started swimming again. I realise now it could have been the shock of quickly switching tanks and not acclimatising it that could have made it worse. I put the serpae to sleep as I didn't want it left dead or dying all day in my hospital tank.

Now the last few days my black phantom that lost half it's tail has started swimming vertically and sometimes loosing coordination/control . Sometimes it's swimming nose up and sometimes nose down. As well as this, one of my lovely male phantoms has suddenly lost a chunk of tail and my golden barbs have raggy tails although I don't know if this is connected to the others or not. 

I do water changes aprox 15% twice a week.

Anyone know what this could be?

Sorry to hear this.
Hope you get to the bottom of it soon.
 

Hi chris I got rid of the shark a good while ago as it was too aggressive. All my dudes now are peacefull. Even the serpae which I put to sleep due to going uncoordinated like the female black phantom is, was actually very peacefull too.