I moved my two 14 year old goldfish into a new 180 litre aquarium last week, ensuring that the majority of the original water was moved into the new tank. Last weekend I noticed some growths on the front fin of one of the goldfish (see photo). Does anyone know what it is and how to treat it?

The goldfish is not bothered by the growths (it is still eating and swimming normally). The KH and nitrite readings are normal. I have just completed a 5 day course of myzaxin, as suggested by my local aquarium shop, but it has not made a difference.

Any advice greatly appreciated. Thank you.

I can only answer briefly/once today but:
* much more importantly than whether the original water was moved over between tanks, did you move the original filter media (+/- the filter itself)?
* what are your ammonia, nitrite and nitrates levels specifically? (What do you mean by 'normal' nitrite?)
The filter media contains the beneficial bacteria that processes the fishes' waste (of which goldfish produce a lot), and this is crucial. If it was not transferred over to the new tank, and new filter media (+/- a new filter) was put in, the fish will be undergoing a fish-in cycle, with ammonia and nitrite presence likely resulting in what looks like finrot. Only 0 ammonia and 0 nitrite, plus nitrates <20 (or no more than 20 above tap water nitrates) will assist in healing - while Waterlife Myxazin is a good medication and what I'd suggest, it won't work if water quality isn't as described.

Thank you very much for replying. The nitrite and ammonia readings are 0 (brand new test kits ordered the other day). I don't currently have a valid nitrate testing kit, but the readings directly from the tap water have always been on the very high side due to using London tap water (this has never been a problem for the goldfish). I transferred the original filter media to the new tank and so I am confident that the tank has not started a new cycle.

After doing some more research I'm wondering if the disease is Lymphocystis? The symptoms are close to what I can see on my fish (bubbly, boil-like growths). Unfortunately there does not seem to be a cure but can be triggered by stress. I'm wondering if the stress of the tank move caused this?

Struggling to reply, so will need to be brief again (apologies- and hope coherent):
* great re ammonia and nitrite, and the transfer of filter media, so can eliminate 'new cycle' aspect;
* lymphocystis a possibility (or an injury in transfer?);
* whether/not tank move may have been stress factor, or whether immune system lowered as fish not young, likely unknown - but focus on keeping optimum water quality for now (see below too);
* re high nitrates, nitrate-removing media often doesn't work but have read favourable comments re some floating plants (if not eaten by fish!), Nitra-Zorb and reverse-osmosis water (latter may be a faff/risk to start experimenting with when got not-so-young fishes' health at stake).

Thanks again for the follow-up message. During today's water change I noticed that part of the injury (the red and white bubble at the end of the fin) had fallen off and was floating in the water. The fin also looks slightly healthier. I've read stories about how the infection can fall off and the fin can self-heal if the fish doesn't experience further stress and so I'm hoping this might be the case for me. My plan is to do a second course of myzaxin in a week's time and minimise disruption to the tank to keep the environment as stress-free as possible.

I'll look into your suggestions for reducing the nitrates. I switched to silk plants a while ago, because my goldfish ate the live plants and created a terrible mess in the tank (it took ages to get the water clear again!), but nitra-zorb sounds interesting.

I have used nitra-zorb pads before, in my tanks, to help reduce nitrate levels. They do seem to work, and can be re-charged by soaking in aquarium-salt water (instructions are usually given on the packet). They eventually have to be replaced with new ones, though. I used to get mine off Ebay, although I'm not using them at the moment.

Thank you for your message oldsplasher. Greatly appreciated. :)