Scatterbrain, this is information I found last year, dont remember where it came from but might help your problem with your tomatoes "Close observation of any changes are critical when growing hydroponic tomatoes. Early diagnosis and adjustment of nutritional disorders is crucial as they rapidly increase in severity and spread quickly.

. Check the colour of the leaves; yellow leaves may indicate that the nutrient solution isn't strong enough or pH is too high, locking out nitrogen - leach and change the solution.

. Leaf tips curl up or red stem may indicate a magnesium deficiency caused by too low a pH - leach and change solution

. Leaf tips curling under may mean the nutrient level is too high - add pH 6.0 water

. A potassium deficiency my cause flowers to fall off before setting fruit - leach and change solution.

Blossom-end-rot caused by too much water puddling in the root zone will create a calcium deficiency - leach and foliar spray with a calcium nitrate solution.

Leaching should be done at every reservoir change to avoid encountering problems. This will rid the growing medium and root zone of toxic salt build up. To leach, rince the root zone with straight pH balanced water. Use twice as much liquid as the hydroponic container would have held when empty.

These are some basic nutritional disorders however, they are easily avoided by using a good 2-part fertilizer, maintaining a correct pH and changing your solution regularly.
Hope this helps,
Grampe

Hi Scatterbrain,

After you recheck the PH and concentration of the nutrient,
try adding some artificial light.
Also the roots need to touch the nutrient solution.
Ciao, Chefmichel