@Sam the Slayer
is correct. It is indeed not calcium but a mobile nutrient. If it was calcium, the new leaves would typically have a definite leaf tip hook downward which I do not see in your photos. I suspect the problem is a lack of available magnesium. Why? Magnesium is a mobile nutrient, which means the plant / stem is capable of moving the nutrient from older leaves to newer leaves where it is needed for growth. Here is one of your pictures that provides some good clues:
Notice the new leaves look good. Good color, flat, healthy looking. Shortly afterwards (Arrow #1) the color has faded and the leaf bending. Arrow #2 shows the leaf margins curling under causing 'cupping' of the leaf and the color has become yellowish indicating chlorosis. Arrow #3 shows advanced stages of necrosis where plant tissue has died. Here is the definition of a magnesium deficiency. Not all plants will show all of the symptoms, however this plant / stems shows several of them.
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, stems are brittle and have a tendency to curve upward. Stems are weak, subject to fungus infection, usually leaves drop prematurely.
We can't really see the interveinal chlorosis due to the red coloration of the leaf. We do see the chlorosis (yellowing) and necrosis as the leaves get older. It looks like most of the oldest leaves on the stem have already died.
With a 5.0 dGH your water is soft. Since dGH measures calcium and magnesium it is likely that most of the hardness in your water is calcium. You could get a calcium test kit and test it yourself, or possibly your local water utility can tell you how many ppm's of calcium and magnesium is in your water. If it were me I would add magnesium to my dosing routine. How?
Based upon your readings I don't believe you have excessive calcium so I would try adding additional magnesium and see if the plants respond. Here is what I suggest:
1) Continue dosing the nutrients you have with no changes.
2) Drop by the grocery or drug store and pick up some Epsom Salt. Get the cheapest stuff on the shelf with no additives, scents, or perfumes.
3) Do an initial dose to your tank of 1/2 teaspoon per 10 gallons.
4) Thereafter, when you do your weekly water changes, add 1/2 teaspoon per 10 gallons of new water added.
Then observe the new leaves as they emerge
over the next two (2) weeks (do not watch the existing leaves leaves - they will not improve and may continue to decline)
. Do the new leaves look greener, healthier, and possibly larger? Has the growth rate improved with the addition of magnesium to your dosing? If so then we are on the right path. As these new leaves mature you should not see the interveinal chlorosis, premature leaf loss, and necrosis develop as you have been. Hope this helps - keep us posted! -Roy