Heya guys I have a couple of seedlings that have yellowing inner new grow leaves, also some bigger fan leaves are yellowing. I am pretty sure its ph lock because of the cold weather and being around 8ph. I have flushed the soil which is a general potting mix with start fert / perlite combo with a very light nute mix at ph 6.2. I have also placed on seedling in a home made heatpad, (used bubble cloner, brink in centre with heater at 24cel. Temps have being low here 16cel day 6cel night. Anyhow going by a chart it looks like a zinc prob which could be from the high ph.
http://www.drugs-forum.com/growfaq/97.htm
http://www.drugs-forum.com/growfaq/97.htm
