Doesn't they make an extension for that unit so you can raise the light higher?

The AeroGarden book does not say to change your water every two weeks, did you read this on some forum?

If you were using liquid nutrients, as opposed to the AG tablets, then it's true - you would change your water every one to two weeks. You do this to replace lost nutrients that have been taken up by the plant.

As the AG tablets are supposed to be dropped in every two weeks and left, this builds up the nutrient levels. If you were to dump your water, then the new mix would be weaker. Not a problem for lettuce, but a problem for larger plants like your tomatoes.

As for pruning, I'm afraid you have no choice. You have to be cruel to be kind, if you don't cut them down then they will grow into the lights and burn. Cutting them down will lose you many buds, but it will also increase shoot development further down the plant, and form buds lower down.

Did you do the prune at week 4/5 as per the book?

Thanks peat much appreciated. I probably read about the 2 week water change somewhere here. As for pruning I read alot of posts here with mixed information, so I decided to experiment. Of three plants I left one alone I pruned the top of another and pruned the sides of the third, but the pruning was probably not enough (think i was timid). I'm going to have to do some additional pruning on all three plants, thanks again.