NFT Canna Aqua Problems

Hey guys

i started a new grow and i my old problems are coming back :(
i'm running a nft system, with 3ml/L canna aqua flores, root excel, cannazyme, and 1/4 tsp Epsom Salts per Gallon
2nd week of bloom just started yesterday
in ppm that would be : NPKMg 139, 80, 322, 47 (+35ppm Mg from the Epsom)
i need to add a plenty of ph- to bring it down to 5.8 (maybe the high amount of hydrogencarbonats isn't so good for canna aqua?)

my tap water values are:
pH 8.0
electrical conductivity (microsiemens/cm) 240 = 0.24 EC
total hardness = 7,3 °dH
carbonat hardness = 7,2 °dH
Calcium ~ 40mg/L
Magnesium ~ 8mg/L
Natrium < 1.0 mg/L
Chloride < 1.0 mg/L
Potassium < 1.0 mg/L
Nitrat (NO2) = 3,3 mg/L
Hydrogencarbonate (HCO3) = 137 mg/L
Sulfat (SO4) = 3,5 mg/L


nft reservoir:
ph is between 5.2 - 5.8 (tends down to the 5.2), ec is @1.8, water temperature is @69°F, 4 oxygen stones are running 24/7
pump is running constant too, cuttings in rockwool
roots are white and fluffy, exploding in growth

every time (no matter if using ro, or 50/50 ro/tap, or just tap water) problems are creeping in again. it seems to start in veg, and as soon as i switch to aqua flores bloom, problems are getting worse
it looks like a Mg-Def (yellow leaves, starting from the beginning of the foliage - tips arent affected) combined with a Cal and Iron Def (small yellow and brown spotts)... with holes in the foliage (not necrotic)
will make some photos soon! that should help diagnosting i guess ;)

is the amount of calcium to few? i read that calcium:magnesium should be something like 3:1
in my mix with my tap water it would be something like 1:1,5
or could it be due to the high amount of potassium? (i read that potassium inhibits the uptake of magnesium..) so i would need even more Mg, but then again the MgCal Ratio is fucked .. hmmm

should i try some calcium supplements ? when yes, how many ppm should i add?
calmag is not avaiable over here.. just Advanced Nutrients SensiCal Grow/Bloom...

could i take some calcium carbonate from the pharmacy, or shall i take a better soluble calcium salt?

any help/feedback or input is highly appreciated :)
thnx guys
 
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