Over-fed? That may be true but why? Why only a couple plants out of the entire crop utilizing the same reservoir? He went to the trouble of stating all the parameters and I think by giving this info, I can now assess what may be wrong other than the generic "It s overfed".
I am no expert so take all this with a grain of salt. I am a mega-grower wannabe.
First off, This is hydro, not soil.
By the leaves becoming flacid indicates an osmotic imbalance where water retention is being lost. So, the salinity/nute concentration of the water must be too high, sucking up the water from the plant in order to equalize. So Yes, overfert, but not necessarily too much nutrient, since other plants are not effected at the same EC levels, which are nominal. The overfert is just these few plants. Why just these few plants?
1) Hydroton , when used by itself and with a drip system, has a tendency to channel the nutrient flow and not disperse evenly so root growth follows these erratic channels. This causes concentrated pockets of high salinity within the grow area. This would also be a random event so it would not effect all plants in the same way. The companys' own brochure states:
"In drip irrigation systems the pellets can be mixed with a medium with better capillary action so the feed is dissipated broadly through to prevent salt build-up."
2) Hydroton will form highly positive ion charges, disrupting normal ionic exchanges, exacerbating the salinity issue. The medium works fine for a few weeks when new, but will build up this ionic charge over time and is not removed with normal cleaning.
They recommend this:
TIP:
"When washing the hydroton before re-using it, it is recommended that it be cleansed with a negatively charged flushing mix, such as Clearex, to neutralize its high positive ion charge."
Clearex will neutralize these charges. I have researched other vendors such as GH, Advanced and Grotek but they do not explicitly state that it is a negative charge solution so the effect these alternate solutions have on charged hydroton is unknown to me. Maybe they do ,I don't know. Here is an excerpt from Botanicare Clearex:
Clearex
A common cause of crop failure can be traced to the build up of nutrient salt deposits in soils or soilless grow media. High salt concentrations in the soil solution cause a shrinkage of plant cell protoplasm away from the cell wall as a result of osmosis. This condition, known as plasmolysis, can eventually lead to irreversible wilting.Clearex is a scientifically formulated isotonic drench solution, which effectively binds with the excess nutrient salt and safely leaches it from the soil. Leaching with tap or deionized water can lead to hyptonic conditions which cause cell lycis with outflow of essential electrolytes and nutrients. This causes tissue damage leading to serious pathogen disorders such as bacterial and fungal infections. Clearex is isotonic, therefore, it creates a safe osmotic environment which allows plant cells to maintain an optimal turgor pressure during treatment.
You will note that not ALL the leaves are cupping, they seem random ? If it were a massive over-nute issue, most of the plant would cup and more plants would also, provided they are the same strain.
I also drip for veg state and (did) use 100% hydroton in 2 gallon buckets. This capillary issue is non-existent in smaller size containers. I have experienced this problem first hand, and found that a good flush with the right agent and to revert to 50% nutes for a week remedies the cupping. Also, in your next grow, if you still will be using drippers, mix the hydroton with CoCo. Whenever hydroton is used in larger vessels, it is recommended to mix with another medium.
