I think if you are using a plant substrate like Laterite or Florite, then root tabs aren't necessary. Either way, I would recommend liquid ferts as well since some plants ingests nutrients through their leaves instead of roots.
Actually after posting this i emailed Hagen and asked what the phosphate and potassium content was in this fertiliser. They said it didnt contain either, but the iron was chelated or something. Cant remember what they said it did though.
Is this bad that the fertiliser doent contain phosphate or potassium? How vital are they?
the tropica plant nutrition (for aquariums with few plants and a relatively large number of fish.) dosent include nitrogen (N) and phosphorus (P).
or the tropica plant nutrition+ (suitable for aquariums with many plants in relation to the number of fish) includes nitrogen (N) and phosphorus (P). )