Re: Very high Nitrite (2-5ppm) and Nitrate (Above 80-160ppm), 0.5 Ammonia - Fish in the tank
#2
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.