Add fertilisers daily for the best effects - plants need little and often for superior growth
Dose according to bottle bearing in mind that as your plants grow they need more food (so you have to dose more)
Ensure good water circulation around your aquarium so all the food is widley dispersed. If your plants aren't swaying in the current, they're not getting any fertilisers.
Any negative plant growth always means you need to add more fertilisers and quickly!
In general you cannot over dose with these fertilisers and even if you do, excess fertilisers DOES NOT cause algae growth!