So, long story short, I had to leave my tank with some elderly neighbours for about 6 weeks. They fed them, but I was only able to get up there to clean the tank and change the water once a fortnight. I gave the tank and filters a clean each time, but wasn't able to check the water and, even if I had spotted any problems, I wouldn't have been able to do anything about it, due to the circumstances I was in at the time. Everything had seemed fine when I'd been up before (the water was a bit cloudy, and the filter was a bit muckier than usual, but I attributed this to fortnightly cleaning instead of weekly), but in the week I went to pick them up, all six neon tetras, and one honey gourami had died.
I got the tank back home about a fortnight ago and broke out the API test kit. Nitrite was at zero and nitrate was abnormal for my tank, but ammonia was through the roof. A bit of online digging told me that neons were particularly susceptible to ammonia poisoning and their gills had been a rather pinkish-red colour.
Whilst I don't really know quite how it happened, I took it to be that my tank's cycle had stalled, so I was left with doing a fish-in cycle to try to get it back on track. For the last two weeks, I've been doing daily 50-75% water changes, and dosing with Tetra SafeStart, because even though I know the results vary, I figured anything was worth a shot. I've not lost any more fish since getting the tank home, and they all seem quite content - swimming and feeding as usual - so I believed I was tackling the problem.
I've been checking the water most days too, and the issue is that my test results seem a bit odd.
To start with ammonia was high, with no nitrite and low nitrate, and the ammonia began to decline over time. Last Thursday, I measured 1ppm of nitrite, and thought I was moving on to the second stage, as ammonia was between 0 and 0.25 (yellow with a slight green tinge), and nitrate was about on a par with my tap water. The next day, I had no nitrite and ammonia was a bit higher than it had been.
It's now been a week, and I've got 0 ammonia, 0 nitrite and 5-10ppm of nitrate. I had the same yesterday and possibly Tuesday, though as said, I'm not great at reading the ammonia, but I had my mother up today and she confirmed the same readings I made, so at least that's a second opinion for today's readings.
Based on the threads here, it seems like 2 weeks is too fast and only having one day with a nitrite reading makes me wonder if something's gone wrong somewhere. Do you think my tank is cycled?