EC @ 900~ Tap Water EC at 360
Ja, did you mean 0.9 nute Ec & 0.36 tap water Ec ?? = total Ec1.26 ? @what Ph ja ??........ as an Ec of 900 would kill em !!................ there are different Ec scales, you got "Hanna", which most use, and truncheon, if you are using the bluelab truncheon etc....... google Ec to PPM conversion chart, you can see the difference there ja ok................. use nitric acid Ph down (Tap water) in veg, and phosphorus PO4 Ph down in flower ok.....
I start my hanna Ec measure for seedlings at 0.3 (Nute Only Ec)................ in final flower i never exceed 0.95 (Nute Only)................ if you see the leaf tip, the first 3mm, start to go yellow, that means you are coming on a bit strong with the nute Ec............... back it back a bit, if you do see this. As to continue will lead to nute burn etc...........
now you have a Ph pen, you can check the health of your soil, around end of veg 5wks, get a 200ml run off from water coming out of the bottom of pot (Run Off)............... take Ph, you want to be between 6.3 and 6.8 at all times ok................ if your Ph drops below Ph 5.8................ the leaves (The Whole Leaf) will yellow with phos deff... google Ph to nutrient uptake chart............ you dont need to feed cal/mag untill the flowering begins, but as you are using (Alkaline Tap Water) you probly do not need to use calcium additive at all !!
Your plant is showing "Stretch" that is, not enough light power on it ok...............if you are using HPS lower it down to a height where when the top of your hand is at plant top, the heat from lamp can just be felt, (26c).......... get an infra red thermometer and check temperature at the plant canopy with that, much easier. it is very handy for checking water temperature is within 2c of the "SOIL TEMPERATURE", use hot kettle to adjust feed before giving etc.....
The infra red hand held temp gauge is also very important to take the soil temperature, soil temp is the most important thing, where nutrient uptake is concerned, as below 19c soil or above 27c nutrient assimilation is deffered !!................. hope that is of some help, ALR