plant leaves looks like transparent

[Teh Teong Chian]

Hi,

I have aquaponic system been running for near 1 year and has already successfully grown lettuce.
So now i tried Choy sum but however the leaves turned kind of like transparent. Anyone can help?

[url=http://s358.photobucket.com/user/toypassage/media/rps20131022_084649_zps435df391.jpg.html][img]http://i358.photobucket.com/albums/oo22/toypassage/rps20131022_0846...[/img][/url]

[url=http://s358.photobucket.com/user/toypassage/media/rps20131022_084722_zps71e93747.jpg.html][img]http://i358.photobucket.com/albums/oo22/toypassage/rps20131022_0847...[/img][/url]

I also provided eddha chelated iron 1 month back. PH of water is around 7.3 as i top up with hard water.
I leave in hot climate country.

[Teh Teong Chian]

pics