Lettuce Woes (thrips?)

For months I've been self sufficient in lettuce for the guinea pigs, using two self watering planters in the conservatory, but they've all become ill as pictured. I've been using a washing up liquid spray and removing leaves assuming it's thrips. They were so badly affected that I pulled the plants and replaced with seedlings, which are now just the same. I'm managing to contain it on the indoor herbs, but getting pretty depressed about the lettuces! You can sometimes see long thin tiny creatures, that are pale green or see through.