First welcome to TPT, that is a nice tank you have there!
I looked at all your photos, downloaded two of them, then enlarged and enhanced them to get better detail. This is the one that caught my eye, I added some arrows to better describe what I see.
First, because this was a 'dry start method' tank some leaf loss is likely due to the transition from immersed to submerged growth. That said, you are correct in that I too see the interveinal chlorosis (Arrow #1; darker green leaf veins / lighter interveinal areas) in the S. repens. Also notice the "puckered" look of the leaf surfaces. You indicated that you are using RO water, what did you use to re-mineralize it?
Arrows #2 and #3 are pointing to leaves with necrosis (dead tissue). The Monte Carlo (#3 arrow) could be due to the transition from immersed to submerged or it could be due to a deficiency. The #2 arrow pointing at the S. repens looks to be too new a leaf to have been part of the dry start and it is showing necrosis along the leaf margin.
The #4 arrow is pointing a a new leaf which is one of the several leaves I spotted with a 'hooked downward leaf tip' which could indicate a calcium deficiency although it may only be sight at this point. It appears you may be using ADA Amazonia as the substrate with is a good substrate and it does contain a little magnesium but it contains no calcium.
I looked at the description for the ADA Green Lightly Minerale and this is what I found:
Green Brighty mineral is a liquid fertilizer supplying iron, magnesium and other trace elements, which are easily depleted in a planted aquarium. These elements are used for growth and pigment synthesis, and the promotion of healthy growth of aquatic plants.
It contains magnesium (although it does not state how much) and 'trace elements' but it does not state what or how much and it does not mention calcium at all. With a TDS of 140 I would hope there whould be sufficient calcium if the tank but TDS measures all cations and anions and it is possible the amount of calcium is a little low - that is why I asked what was used to re-mineralize the RO water.
Assuming that is ADA Aquasoil is the substrate, and you are dosing potassium, minerals, nitrogen, and iron it is likely that potassium, nitrogen, nor iron are deficient. I was first inclined to suggest dosing just the magnesium as I did in the thread you referenced however with the hooking leaf tips I think you would be better served by dosing a GH Booster that contains calcium and magnesium. If Seachem Equilibrium is available where you live I would recommend that. If not, TNC GH Booster
would work or you can mix your own using Tom Barr's recipe:
2 parts: K2SO4: potash of sulfur
1 part: CaSO4: Gypsum
1 part: MgSO4 Epsom salt
Might be easier to find those and make your own.
Buy say 1-2 Kg of each that is powdered and mix.
If using Equilibrium I would do an initial dose of 1 teaspoon per 10 gallons. Thereafter, when you dose water changes dose 1 teaspoon per 10 gallons of new water added. This should increase the hardness of your tank by about 2.0 dGH and add sufficient magnesium and calcium to cause a noticeable improvement or eliminate the deficiency symptoms. Sometimes it takes more that the dose I suggested but let's do this for two weeks.
Now the hard part.........waiting! Watch the new leaves as they emerge for the next two weeks; do not watch the existing leaves....they will not change.
What you should see is the new leaves look healthier, do not have the 'puckering' we currently see, the hooking of the leaf tips should diminish, and the rate of stem growth may increase. As these new leaves mature, they should not develop the interveinal chlorosis or necrosis that is happening now.
Keep us posted as things progress! Pics are always appreciated! -Roy
I. Symptoms appearing first or most severely on new growth (root and shoot tips, new leaves)
A. Terminal bud usually dies. Symptoms on new growth.
2. Necrosis occurs at tip and margin of leaves causing a definite hook at leaf tip.
Calcium is essential for the growth of shoot and root tips (meristems). Growing point dies. Margins of young leaves are scalloped and abnormally green and, due to inhibition of cell wall formation, the leaf tips may be "gelatinous" and stuck together inhibiting leaf unfolding. Stem structure is weak and peduncle collapse or stem topple may occur. Roots are stunted. Downward curl of leaf tips (hooking) occurs near terminal bud. ammonium or magnesium excess may induce a calcium deficiency in plants... calcium deficiency
Differentiating between calcium and boron deficiency symptoms: When calcium is deficient, there is a characteristic hooking of the youngest leaf tips. However, when boron is deficient, the breakdown occurs at the bases of the youngest leaves. Death of the terminal growing points is the final result in both cases.
II. Symptoms do not appear first or most severely on youngest leaves: Effect general on whole plant or localized on older, lower leaves.
C. Interveinal chlorosis. Interveinal chlorosis first appears on oldest leaves.
1. Older leaves chlorotic, usually necrotic in late stages. Chlorosis along leaf margins extending between veins produces a "Christmas tree" pattern. Veins normal green. Leaf margins may curl downward or upward with puckering effect. Necrosis may suddenly occur between veins. Potassium or calcium excess can inhibit uptake of magnesium...magnesium deficiency
When the external magnesium supply is deficient, interveinal chlorosis of the older leaves is the first symptom because as the magnesium of the chlorophyll is remobilized, the mesophyll cells next to the vascular bundles retain chlorophyll for longer periods than do the parenchyma cells between them. Leaves lose green color at tips and between veins followed by chlorosis or development of brilliant colors, starting with lower leaves and proceeding upwards. The chlorosis/brilliant colors (unmasking of other leaf pigments due to the lack of chlorophyll) may start at the leaf margins or tips and progress inward interveinally producing a "Christmas" tree pattern. Leaves are abnormally thin, plants are brittle and branches have a tendency to curve upward. Twigs are weak, subject to fungus infection, usually leaves drop prematurely.