start of a calcium or magnesiom problem?

hey guys,i have been growing these plants in 11 litre pots,using canna professional soil and canna nutrients,the lights i am using is the spider farmer sf1000,i am growing 2 of the same plants but one has shown signs of a problem recently,the other plant is doing fine,they are 5 weeks old and just going into flower now,they are autoflowers so i have been giving them low doses of feed,now they are on the 4th feed,i increased slightly with each feed,the last feed was 4ml of canna veg to 5 liters of ph water,6.5,i added 4ml rhizotonic and 3ml of canna cal/mag,this was going to be the last feed before i change to flowering nutes,the leaves have turned a rust colour and a couple of the fan leaves have small brown spots on them?,im wondering if this could be a deficiency starting or mabye from the light?,ive not seen these before and out of the 2 plants,the other one is fine,,any ideas?,,thanks in adavnce

yes it's calcium
how must ppm/mS test your tap water ?

thanks kingromano,yes i jst measured the ppm and its at 220ppm, could this be calcium toxicity or lack of calcium?,i was using a light dosage of cal/mag up ontil now, at 2.5ml to 4 litres water,ph of 6.5,ive jst flushed them with mild veg nutes and no calmag this time

you can't really flush soil, flushing is for hydroponic medias

some elements are immobile in the soil while other are not, by flushing you just create more imbalance

0.3mS of tap water+calmag should be enough for vegging plants. they dont have high Cal needs at this stage

your plants are pretty dark. only thing i see is the soil is too hot ( too much fertilizer accumulated in it), then ph is too low.

try to water with your regular feed at ph 7

thanks for your help kingromono,ill give that a try