I have been using Amazonia for the last 6 years in 5 different tanks, from 30-120 g. I do EI, co2 etc. spent more than 2k$ on test equipment , colorimeter, light meter etc. my observation been that all my tanks do extremely well for the first 6 month, then things slow down and stop growing. Tried every thing from increasing co2 , fert , light , etc...nothing happen. The only thing that will work is to use new soil. Works like magic . My theory was the organic waste build up in the soil was the issue which I can never fix with deep vacum . So for my last tank 120 gallon I used 4 nuclear filters (yes 4) , with iwaki 40., and 2 AM1000 for co2. Results was the same. Tha hair grass covered heavily for 2-3 month had to trim weekly now I may do it once a month the stergun had slow start but came around nicely and now stopped growing ior I should say it slowed down after 6 month. I went back to basic , the tank is always will termed . Measured the light at the bottom was the same . For the fun of it removed some Aqua soil from an area about 10x10 in . But fresh soil and replanted some of the hair grass and stergun , they grow very well in that area. I really have no explanation for that . I wonder if any one able to sustain a tank with Aqua soil for more than a year with some of the delicate plants. Thanks