TDS and pH are two separate readings. There are meters that can do both, but they're not cheap. A cheapie TDS meter can be had on ebay for around $20. I can't stress enough how important it is to have one, otherwise you don't really know how strong your nutrient solution is. In the meantime, try running the drip a little less frequently, maybe 15-20 mins per session instead of 30 and see if your plants respond well.