For good fertilization it is necessary to respect dosages and administration times. Just try it:)
For example you can use this product (I had good results with these):
dennerle fertilization protocol
- S7 (every week)
http://dennerle.com/en/products/aquaristic/plant-care/basic-fertilization/s7-vitamix - E15 (every 2 week)
http://dennerle.com/en/products/aquaristic/plant-care/basic-fertilization/e15-feractiv - V30 (every 4 week)
http://dennerle.com/en/products/aquaristic/plant-care/basic-fertilization/v30-complete
remember that you should create a tank with a lot of plants. The more plants you put the less are the problems :)