The plants look fine to me but they seem awfully small for being 5 weeks in.
Get a PPM meter and use it. I do not do rez changes without a PPM meter. Different plants can handle differemt levels of PPM's. I've got a plant I can push all the way up to 3000 PPM's without a problem, while I've grown some plants that can not go over 800 PPM's. I currently use Botanicare and my nutrients consist of Pure Blend Pro, Cal Mag, and Liquid Karma. If I'm changing 2 5 Gallon reservoirs I'll mix nutes according to the bottle for 8 gallons. Even mixing for 8 gallons the nutrient mix would push my PPM's to almost 2000. If you hit a White Widow plant with 2000 PPM's you would knock that thing dead in a matter of days.
When running new strains I usually start the nutrients around 600-700 PPM and work my way up from there. I would recommend you do the same. TDS meters can be purchased online for under $30.00 and they are money well spent. You'll be able to try new things and push your plants to limits if you have a TDS meter.