my 4 week old plants lookin sick

i have four chronic plants about 4 weeks old grown from and about 5 days ago i started seein little yellow spots on the leaves it seems to have got worse and is covering the leaf. i put a piece of white paper under the plant and gave it a shake, there was tiny little yellow bugs on the paper. can any 1 tell me whats going on plz. i didnt really understand the troubleshooter form but here is what i no: planted in coco soil with nothing added, kept indoors with 20 hrs of light a day, fed with tap water that has been left till room temp with added canna part a and canna pt b 5-10 ml each daily, 600 watt light which is about a foot away from plants. changed from a 150wt halogen light a week ago, room temp is averaging 27 degrees, i have 2 extractor fans and an interior fan. i am new to all this and i am just going on advice from other people. any advice will be gratley appreiciated as my littlens av cost me alot of time and a few quid and it will be a shame 2 lose em now

not sure about the bugs, but the plants look really stretched. a plant "stretches" looking for the light. this could mean a couple of things for you. the first being, your plants spent so much time trying to get to the light, that they didn't form a healthy root structure. not good, they'll probably die. to fix this look @ your lights. make sure you have them as close as possible without burning the plants, and you might want to check the color temp etc...my signature has a link to a really helpful thread on lights. I did notice tin foil on your setup, tin foil is not really recommended because of heat and conductivity issues, try some flat white paint.

hope this was helpful.

thanx for your help it is really appreciated. i have ripped all the tin foil down and i will paint it matt white later on. i have been swatting up, havin a good look at the website for tips and im thinking my light should be 5 in away from the top of the plants. is this right?

If the 150 was a halogen then that's why the stretch. halogen bad. I hope the 600 is HPS, high pressure sodium or MH, metal halide.. Going from a 150 to a 600 is alot of stress. Sorry but they kind of look like a lost cause.. If you can take the top of it for a clone cutting and you will be better off than starting from seed again. 2 weeks for clone and you could have a nice little plant ubder the 600.

it may be a shame to lose them, but using a halogen light is bad just like said above....If your a beginner maybe you should try something simple first like CFL's or at least invest in a metal halide....If my plants ever stretch that bad I'd rip them up in a skinny minute....Trust me you'll be more unsatisfied trying to mess with it, then starting over and doing it right.....4 weeks of growth doing it right could have a bushy plant at the same height with multiple branches then a anorexic plant that looks like it's having trouble breathing.:D

So basically what I'm getting at is:

1.) Rip them up
2.) Do a little more research on lights and what kind for your setup
3.) Start over and do it again with hopefully better results!

Other than that, Good luck with w/e you decide to do!

Lol Pete you'e gotta be kidding us? I'm still laughing as I'm typing this. Those plants are worthless. Dump them now and bin the halogen so you're never tempted to use it again. That's up there with the worst cases of stretch I've ever seen. :)
The pictures of the soil and general area from what I can see look otherwise reasonable. Start germing some new seeds, get a couple of 23watt+ 6500K compact fluorescents like Italiano said and keep them 2-3 inches away. Once they get some foliage energy behind them you can switch to the 600Watt HID and they'll explode.
Start a grow log when you do it so people can help you along the way. In this instance it would have saved you 4 weeks and a few bucks on the power bill.

after reading the first post i lowered my light and ripped down the tin foil. i got rid of the dead leaves. four days on and i have seen a massive improvement, new growth all over the top of the plant and down the stem. if there is no hope for these plants how do i go about cloning so i can salvage something. i have researched it but i have found so many ways of doing it and dont no which 1 to try. thankyou all for all your help!