first time hydro brow/rust patches on top of plants

[R4st4]

hey, i got a aerflow system, 20 plants, they been there 5 weeks in 12/12 and r aboute 60-70 cm tall, the rust patches on leafs on top of the plants started after 4 weeks, then the ec was around 1.6-7 and ph around 5.4 to 6 i thought it was to nute burn so i changed the res and and lowered ec to 1.4, but im not sure anymore because it getting worse... some leafs have got yellow dots now, checked ec today it was 1.2 now
but only the top part of the plants that r affected

im using gh flora 3 part and thought of adding pk13-14 this week
res temp 17-21 C
room temp day: 22-24 C night: 17 C
humidety 40-60 %

 

[scegy]

this is probably a ph fluctation problem and the sudden ec drop,
you must maintain the ph in the limits od 5.6-6.1, anything above or under will hurt ur plants in a way it already did
also chainging the water at this stage is like transplanting at the same stage in soil, avoid doing that, just remove some of the solution and replace it with pure water next time, untill you get the right ec/ph and not the whole res

consistancy in a matter of ec and ph is most wanted in a healthy root system

nice plants otherwise man!

 

[stinkfinger]

looks like a calcium and or magneseum deff. Go get some cal/mag to fix the problem

 

[heavengrower]

Them leafs are very green !

 

[R4st4]

hey..

scegy: the rust spots where there b4 the ec drop...i did the change because of the spots, i thought it was overferting and it can still be tho, ph is stable...never been under 5.4 and not over 6

stinkfinger: yea calcium was my second on the list but thers no sign of magnesium def.
pics r lying abit, i got both magnesium and calcium in liquid form, but not added anything.

new pics