The root tabs will not have much impact over Flourish Comprehensive liquid with stem plants. Substrate fertilization is usually beneficial for substrate-rooted plants, by which I mean swords, crypts, Vallisneria, Aponogeton, Sagittaria, lily types, and so forth. These plants all have extensive root systems that remain in the substrate, and providing nutrients directly or close to the root systems will most benefit the plant.
Stem plants usually produce roots from the nodes along the stems, where leaves are also produced. Some stem plants do this much more aggressively than others, but in either case the nutrients must be in the water column to best benefit the plant. Many stem plants also assimilate nutrients through the leaves too, another advantage for using liquid fertilizer. And Java Fern assimilates best from the water. Adding substrate fertilizers may help some of these a bit, but the most benefit will certainly come from liquid fertilization and Flourish once weekly should suffice.
A word on Laterite. This is simply an iron-rich clay, so its benefit is limited to providing iron at the root level. Same scenario as above applies. Substrate-rooted plants will most benefit from this, but as only iron is involved, care must be taken not to raise the iron level beyond what the plants need. Iron is a heavy metal and highly toxic at increased levels. Plants might have difficulty with this, depending upon other nutrients. I used a layer of Laterite in one tank many years ago, but noticed little if any difference. I have since learned that supplying only one nutrient is not likely to benefit plants, unless that is the only missing nutrient without. And more importantly, an excess of some nutrients can cause other issues for plants.
Last edited by Byron; 01-09-2012 at 08:05 PM..