Nothing fast about low tech tank's in my view.Soil can provide nutrient's a bit quicker than plain inert gravel, but unless you mix in some clay with the soil to help hold onto nutrient's a bit longer,,,the soil's can peter out after a year or less.
Fine gravel with root tab's,water column fertilzing,is much less messy than soil and plant's can do fine with this approach.
So to answer the question,, does soil = faster growth? I have tried both way's and growth for me was about the same over the long haul, with perhap's a bit better growth intially from the soil depending on it's content (peat,clay, plain old top soil,Miracle Grow Organic potting mix.)
My biggest detriment is lack of CO2 injection or supplement's such as Excel,Glut,Easy carbo ,etc.
I am limited by low light, low tech method to less light demanding plant's which thereby require less CO2 to do well.Is the light being used that drives the demand for everything else.
I think I'm going to try a few options to see what works the best. I like the idea of the root tabs though, seems a lit cleaner, but dirted tanks seem to grow really nice.
I'm going to setup a rack of 4 40B tanks for growing eventually. I'm waiting for the next $1 per gallon sale though.
In the meantime, I'm going to test out different combinations of substrate to see which works the best and/or is the cleanest.
So I will have six tanks setup (4 10G's, a 20G, and a 29G). I think I'll do something like this:
Play sand and root tabs
Gravel and root tabs
fine gravel and root tabs
Play sand and dirt
Gravel and dirt
fine gravel and dirt
Since I have everything, it won't be that hard to do. I won't really be testing the same plant in each tank, but I think I will get a good general idea of what is working and what is not. All tanks will have high lighting, high co2, and dry ferts.
Just waiting for my CO2 tank to come in next week and then I can get started.