I'm so glad it isn't just me! I've been reading plenty of old threads etc and I just can't seem to crack it at all. I'm hoping it is just the lack of oxygen that is stopping them grow quicker.
I've put the heater on to 28-30. The thermometer says it is sitting between 24-26 but it is one of those black strip ones that I got pretty cheap online so I'm not sure I trust its accuracy...It said the same when I had it set to 25.
Got my 30cm airstone and it is ploughing air happily through the tank now. Had it on for a couple of hours last night and got it on again for a couple just now. Ammonia is at around 2ppm (I suspect the drop from 3 is because of adding 4L of water to the tank) and nitrites are still at 0ppm.
Sounds promising! Sometimes when a cycle is slow to get going, the nitrite munchers can arrive and start work on the first little bit that's produced so you can get a drop in ammonia without a corresponding spike in nitrite. Hopefully, that's what's happening in your case. Test again tomorrow and if it's dropped a bit more, top up to 3ppm.