Hey Skatter- I never had any problems with my recirculating method. Just calcium problems late in flower, but that was because I backed off on the calcium. I could never really measure any accurate readings of ppm once it began to recirculate. I would just make a new res every time it ran out of water. I think the key to recirculating is to allow the feedings enough time to properly flush the soil every time. My feedings were 15 minuets long so the coco was flushed every time with fresh oxygenated nutrients. This grow will be different because I bought a digital timer that allows me to do feedings at a minimum of 1 min. So this grow will be a little more like DTW. My first update will tell all the information on this. I will be doing the update later tonight.