Something I've pondered occasionally keeps coming back as I read through @burr740
's excellent thread here and @Saxa Tilly
's rotala kill tank over at the Barr Report - does it make any sense to attempt to feed plants via "under substrate feeding"? "sub-substrate feeding"?
I'm considering trying an experiment to see if if would be possible to inject liquid ferts under the gravel, allowing them to slowly filter through the substrate and to the roots via osmosis. Presumably some amount will also get into the water column, but there would be more at the roots. I know, I know...just use dirt...aquasoil, etc. But there are plenty of cons including the mess and the (relatively) limited lifespan. There's also O+ or root tabs in an inert sub - less mess, but those also run out.
I'm thinking of setting up a test tank. Retrofitting something like an old undergravel filter, overlaying it with a fine mesh, running a few tubes from peristaltic pumps underneath, then layering over the whole thing with some extra Flourite I have laying around. One of those dual TDS meters with one line underneath the sub in the UGF and one line in the main tank should tell me how quickly the ferts injected under the sub end up in equilibrium with the water column. Assuming it's relatively slow (a day or two?), that would mean that the roots in a heavily planted tank would have a reasonable "first dibs" period. With the right balance, theoretically you could have a setup with an indefinite life span, with no mess, that shares many of the same advantages of a dirted/aquasoil tank.
Anyone know if anything like this has been done you could point me to? Any obvious reasons why this is dumb? One thing I know I need to test out is whether a peristaltic pump can handle the head associated with pumping underwater.
Thanks for any insight you have!