Not sure about the EC, but maybe try lowering the water temp to increase Dissolved Oxygen
http://www.ecy.wa.gov/programs/wq/plants/management/joysmanual/dissolvedoxygen.html

Perhaps 65-70d egrees F

I`d cool the res and make sure there`s enough humidity in the room to go with the air temp. If there`s not enough RH, it can limit transpiration causing water stress which can look like nute deficiencies. In reality, the plant hasnt enough water moving through it which limits the supply of nutrient. Symptoms that look like calcium deficiency are usually the first to show up as its one of the slower uptake elements.

Thanks for the replies. I'll put some ice blocks beneath the reservoir and see if that helps.

I just came back from Hong Kong and visited in Kowloon some hydroponic shops and had shared some knowledge between both our countries and similarities,your temperature is no higher or humidity higher there than in Brisbane , so I dont know about ice blocks I have never used ice or anything to cool my nutrient mix as your temperature is similar to ours eg Sub Tropical.I have grown Pak Choy very successfully using the following range Pak-choi ph 7.0 15-20EC they prefer a very neutral PH and an Ec on the higher scale. I see a lot of people in the USA using a lower PH and lower EC but in a similar climate to yours I have had success in the scales given.

Thanks Robert, I hope you had a nice time in Hong Kong! You might have seen where I lived since I live right next to the airport, and if you spotted super bright lights by the window in one of those buildings, that's me and my DWC, haha. Thanks for the tips, I'll raise the PH and EC and see how it goes.

I think Robert is talking about CF, still common in Australia, not EC, check with him beforehand...

EC x 10 = CF

My comment on the original question is to give the plants a breeze with a small fan.

This post was edited by PupillaCharites on Sun, Apr 6, 14 at 22:29

PupillaCharites you are 100% correct I did not want to mislead anybody the EC is 1.5 to 2.0
Microlab please use the EC as shown now so sorry I get so used to working with my trunchion metre that I gave the incorrect scale.

Yes, I thought you meant 1.5-2.0 :-)

I changed out the res yesterday; when I added enough nutrient to make EC 1.9-2.0, the PH went down to 5.8 without the use of PH-down. I'll just see how it goes, if the plants don't do well, I might need to get a bottle of PH-up to raise the PH a bit.