House & Garden Roots Accelerator

Top selling root stimulator from House & Garden that not only encourages rapid root development in the early stages of plant growth, but also acts as an effective guard against root disease in re-circulating hydroponic systems.

Looks expensive, but has a very low dilution rate and so is in fact probably the cheapest root stimulator of note on the market. 

Dosage rate 0.3ml per litre of nutrient solution.