Thoughts on my setup?

[ematt]

Hi all,

This is my first venture into hydroponics, and also my first post! Great to be here right now.

I've just started experimenting with hydroponics, growing a few lettuce seedlings. They're seeded in 1 inch rockwool cubes.

I had some early problems with white gooey stuff on the bottom of the rockwell cubes (I never worked out whether it was fungus or algae). I noticed at this time that the nutrient solution was rather warm, and so I've designed my system with a cooling mechanism, and have had no subsequent problems in this area.

I have had some other problems though, and I'd be grateful for any thoughts. Before proceeding though, a little more about my setup. I do like a little animation, so I made one for you so you can see exactly what I've done. You can view it here: www.youtube.com/v/t_94rkgyKnU

My lettuces are growing, but I'm suspicious they're not doing as well as they could be. Here's a photo of what they look like now, at 22 days since sowing (the red lines show you the size of the tin foil covered square base, to give you a feel for scale):



They seem to be a bit "wilty", and they each only have one tiny, thin root, about 2-3cm long, emerging from the bottom of the rockwool cube. I had imagined that by now they'd all have a nice bunch of roots emerging. I can see a few roots protruding from the edges and the top of the rockwool cube. So it seems there's definitely root growth happening, just not outside their tiny rockwool cube. My guess is that I'm not providing a humid enough environment below the rockwool cube. Maybe the draining of the nutrient chamber sucks in dry air from the room, which limits root growth. Any thoughts?

I guess a better system might be to keep the water cool with a thermal syphon instead of gravity syphon, as they do with passive solat hot water systems. My main concern is that I'd not be providing enough mixing to keep oxygen levels high enough. Does anyone know where I can read any guidance on how much mixing is enough mixing? E.g. recommended flow rates from certain heights for a certain volume of nutrient solution? I imagine it depends a lot on your system, but it would be great to see examples of what isn't enough, and what is enough!

Another problem might be lighting. I'm in Greenland, so am planning ahead of the dark winter coming and am using a metal halide light. I am using a 150W bulb, and a V-reflector held at a height of 40 cm above the base of the plant. I have a lux level meter that says the illuminance on the plants is about 15,000 -> 20,000 lux, and I keep this on for 16 hours a day. I know illuminance in lux is not a suitable indicator to understand how much usable light the plants are getting, but the lux meter is all I've got I'm afraid! Does it sound about right? I could lower the lights more, but that seems a bit intense.

Many thanks in advance for any thoughts/advice you might have, and of course, happy to answer any questions!