Well been having a tinker with the tank today. Done a water test to check parameters. They were as follows
pH- between 7.2 and 7.6 so it is going down which is good.
Ammonia - 0.0 ppm
Nitrites - 0.5 ppm so water change necessary
Nitrates - 5.0ppm
So had a 25% water change and retested my nitrites and nitrates
Nitrites- 0.25ppm
Nitrates -5.0 ppm
So I'll have another water change tomorrow as I don't have time due to the filter system as it comes in at a trickle takes hours to refill from 25%.
My crypts are melting, which isn't unexpected but they seem to have new growth on a few so that's a good sign the hairgrass is starting to put root runners onto the gravel which is equally a good sign that they are getting "enough" light.
So the API fertilizer seems to be working but when I need to add 40ml every time I dose I'll go through bottles quickly which will be costly.
Cardinals out exploring just need some tank mates.