You can see clearly where the old sediment is (16 months old) and where the new sediment has been added. I left a layer of old ADA Aqua soil on the bottom 1", then added about 3x this amount on top and sloped up towards the rear.
The vertical height difference is 11 cm.
Tank is 20"H, 24" L: 18" D, 38 Gallon rimless. You can see the filter intake and outflows. Light is 80 micromol 12 ours a day and will be reduced to 70 micromol and 9 hours once flooded.
You can see dramatic differences between the older ADA As and the new. I' had the idea to seed the new with old, looking back, this was a mistake.
I added liquid ferts to the spray bottle, so the front edge is coming back. I also got BGA quickly. I added some EM to the spray bottle and hit it for 4 days to kill it back (entire tank, not just the front).
The difference between the rates of growth and leaf size is very apparent(not so much in the pics here, but a little). I disturbed the front edge some, but it was a mess and I vacuumed up the older soil where there was no rooting. Nothing would grow well there. I figure it will fill in well once the tank gets flooded and run down to the nub where the front and bottom glass meet. Never liked the look of sediment on the front panel and will give a nicer slope look.
The growth rates will equilibrate later once the tank is flooded because I add ferts to the water column and the sediment will leach nutrients everywhere.
I did not predict the ADA AS was that depleted, but.........it really was a huge difference. So I'm doing a pot test later at the lab to see.
You can test and see the differences in nutrient depletion between the old and new ADA AS. Yes, there's still growth at 16 months, but's about 10% of the new ADA.
Anyone wanna buy 30 lbs of old 16month ADA AS from me?
Argghh, I'm a lousy salesman ain't I?
You can do pot test in terrarium settings to isolate the sediment/water column interactions, address the CO2 issue, so that the test is independent of other factors other than sediment fertility.
This way you can compare them and their effectiveness to grow various plant species. It's also easy, cheap, no water changes, CO2 fiddling/assumptions etc, no added light if you place them outdoors etc.
You can sample older sediments vs new, sand, flourite etc
You can also add sprays of foliar nutrients to simulate water column uptake also.
So the test at the lab should help address the question as far as growth weights based on dry mass. I'm not going to do tissue analysis etc. Nothing to involved. And........ I have plenty of old depleted sediment to try and do something with now. Sure ya do not wanna buy some?