It sounds like you have been given advice on what you can do if it's whitespot - there is a non-medication approach or a medication approach, or both can be tried. Cf https://www.fishkeeping.co.uk/articles_88/white-spot.htm and https://www.practicalfishkeeping.co.uk ... a-problem-like-whitespot/ *However*, I'm not convinced (yet) that it's definitely that, hence the suggestion of eSHa 2000, eSHa Exit, or the combination of both which gives the best chance of zapping whatever it is.

Lil2606 - hope you're not too disheartened with the problems you've found yourself with. It's a brave undertaking, moving into rented accommodation and simultaneously taking on a tank that the owners have left you with, but you're doing your best to improve the situation by upgrading to a larger tank, attempting to save the female that was experiencing problems, and planning to add to their shoal in future, etc.

I can understand why you bought a new female to replace the one who died and give the male some company, to ensure that you didn't lose the filter bacteria that was building up, and your rationale to add to the shoal in the future. However, as you've concluded yourself, best to delay getting any more fish until well after the fish-in cycle is safely completed, and concentrate on that over the next couple of months and keeping the two fish you do have healthy.

Hopefully the link that Fishlady provided to help with the fish-in cycling, and on treating them in the main tank to ensure it rids the tank of any whitespot. As N-HoneyGourami says, you could start doing a fishless cycle on the quarantine/small tank, to prepare it for future fish which you could quarantine in there for a month before moving into the main tank - the link for it is here https://www.fishkeeping.co.uk/articles ... hless-cycling-article.htm . [When you do move them into the main tank, move across the filter as well, so that there will be sufficient beneficial bacteria to cope with the new and additional fish. However, we can guide you through that when you eventually get to that stage of buying new fish. Personally, I've found Pets At Home fish fine - like any chain, some stores are better than others.]

Hope that helps.

My first aim would be to get the ammonia down to 0. Your post and the 0.25 reading rang a bell with me and, skimming through your old posts, it looks as though you did manage to get this down/close to 0 for a while but it's been back up since. Does your water conditioner address the chloramine that your tap water contains (eg Seachem Prime)? If not, I'd definitely use that.

As for what it is, it's difficult to tell. If it were fungus-like, then I'd probably give eSHa 2000 medication a go. Another possibility is whitespot (sugar/salt-like grains) or velvet (dusty gold/brown), and eSHa Exit addresses both. These treatments can be used together if required.

Yes. :)

What is your tap water ammonia level? It really ought to be 0 in the tank. Does your water company put in chloramine, and, if so, does your water conditioner address that? What is your tank and filter maintenance regime? I'm just wondering if / hoping that if we can get your ammonia down to 0, and (if) that might make the difference and resolve the problem.

Sorry to read about this. You absolutely did your best for her. Fishkeeping is very 'trial and error', and often when deliberating over potential courses of action, it's very easy with hindsight to have wished that the alternative course of action was followed. I'll have to postpone the rest of my reply until another day but I'll elaborate then to illustrate.

There isn't really "the best" as different filters have their own respective pros and cons. However, Fluval and Eheim brands generally have a good reputation.

The strips are far from accurate, and the ammonia strips are particularly difficult to read. Liquid-based test kits would be worth the investment, to help us to help you get to the root of the problem. I like JBL.

Sorry to read about this. From your description, I would have thought he'd ingested some gravel. It's possible it may have gone further back / been swallowed, and he may try to pass it out the other end.

What are your readings for ammonia, nitrite and nitrates, using a liquid-based test kit? Although you haven't changed your tank maintenance regime, it's possible that the water supply maintenance has altered a bit, which can sometimes lead to alterations in water quality.
Does your water company use chloramine and, if so, does your water conditioner address that?

I think this is almost certainly the result of living in such a small environment (the nearest analogy being a dog kept in a kennel rather than taken out for exercise) and likely the effect of ammonia, nitrate and high nitrates. A liquid-based test kit to measure these three aspects of water quality is vital (hopefully that's what you now have?), in addition to the larger tank - and it will be particularly important to monitor these if additional fish are added.

Until you get the larger tank and appropriate test kit (if that's not what you have already), do daily or twice-daily water changes of ~25% to improve water quality - these need to be at 0 ammonia and 0 nitrite and no more than 20 above tap water levels for nitrates. The combination of the larger tank and maintaining water quality as described will hopefully resolve the problem (and make it less likely that she is fin-nipped).