Don’t flush with anything and plan P H water that’s it. But yes you are catching it early.
It still could be a couple of thing and one could be this. your’s is earley stage so it’s more
.difficult to figure out just what it is.
This pic is very similar to yours but in a later stage of > Manganese
And then there’s this one> Potassium
This one here is BROWN SPOTS
Now please read this cause I believe I got this thing figured out.
A magnesium deficiency, as manganese deficincies are mostly characterized
by interveinal chlorosis which is a yellowing of the leaves between the
veins with the veins remaining green. The browning spots is called marginal
necrosis which is usually caused by a calcuim or magnesium deficiency.
A magnesium deficiency can be quickly resolved by watering with 1 tablespoon
Epsom salts/gallon of water. Until you can correct nutrient lockout, try foliar
feeding. That way the plants get all the nitrogen and Mg they need. The plants
can be foliar fed using ½ teaspoon/quart of Epsom salts (first powdered and
dissolved in some hot water). When mixing up soil, use 2 teaspoon dolomite lime
per gallon of soil.
If the starting water is above 200 ppm, that is pretty hard water, that will
lock out mg with all of the calcium in the water. Either add a 1/4 teaspoon per
gallon of epsom salts or lime (both will effectively reduce the lockout or invest
into a reverse osmosis water filter.
Mg can get locked-up by too much Ca, Cl or ammonium nitrogen. Don’t overdo Mg or
you’ll lock up other nutrients.
Calcium deficiencies are difficult to distinguish visually as excess calcium may
produce deficiencies in magnesium and potassium.
Now I say do the Epson Salt thing and give it some time and I do believe you’ll be a happy man.