PH is 6.0
Reservoir temp 64 F
Lights two 42W CFL (2800 lumen each) 18 hours on, 6 off
7 gallon Reservoir with 12" airstone with a pump rated for 50 gallons.
Nutrient used is Dyna Grow. 3 tsp per gallon as per instructions.

I don't own an EC meter yet. Do you suppose the nutrients are too strong for young lettuce??

I need to act fast on this to save my leafy friends.

Thanks for any suggestions.

I have looked up the Dyna-Gro range, I assume you are using the Dyna-Gro Grow product and not any of the others? This is what you need for your lettuce, vegetative growth.

When you grow from seed or start to grow using small seedlings then the EC must be at a reduced rate. By feeding them the full 3 tsp you are giving the plants the maximum amount of grow product - this is going to be way to high for your small plant.

Now, Dyna-Gro (as far as I can see) don't give dosages for starting out, this is bad... You have no way of telling what you are putting into your tank, unless you buy an EC meter.

If you can get hold of a meter the battle is won, you will then be able to give the right amounts of nutrients to your plants.

Lettuce, generally, don't like high EC levels, they are a 'delicate' plant. When in full swing would I put no more than 1.5 into your iceberg.

In the interim, you are a little stuck. You could 'flush' the system through for a few days using pH water (adjusted to 6.0) to remove the excess nutrients. You can then reduce the amount from 3tsp to, say 1tsp, and see how this goes but, again, you can only guess your EC - which is impossible...

From what I can see, you are doing everything else perfectly. Sort yourself out with an EC meter and you will have all the tools to do hydro. really well.

There is one more alternative, purchase a better brand of nutes that tell you how much to add during the stages of growth e.g. General Hydroponics, general dose is 1 tsp going up to 3 tsp for the grow mixture.

Here is a link to other links showing EC and pH growing tables: http://tengreenthumbs.com/?p=586

The one from Bluelab in my opinion is pretty spot on and is the one I used when I grew lettuce.

Lettuce will grow fine for a while with nothing more than tap water as long as there is calcium in it. My tap water has an EC of 1.2 fresh out of the hose!

With lettuce, less is more. Go easy on the nutrients; if you don't you'll experience 'tip burn' as well as brown roots.

Clean your container with a wash cloth and soap and water, make sure there is not soap left as you rinse it very clean.

Add water to the level where you normally operate your container, drop in your air stones and then slowly add your nutrients until you get to about .5 EC.

When you get there check your PH. For lettuce, anywhere between 6-7 is okay. For me, I set the PH to 6.0, and then it should creep up to 7.0 over time. When it gets to 6.8 or so, then remove the lid and add PH down to get back to 6.0.

Many folks add the PH up or down or change the nutrients while the plants roots hang in the water. This can cause your plant to have issues.

Also, if you spill your nutrient solution on the leaves, they will also turn brown or yellow.

If your roots are white, they are getting enough air. If they are brown / rotting then they are not getting enough.

Make sure clean the media very well before using it, and if you are wise you will flush the media each time you change out your nutrient solution.