I've read on here that Promix has a very high ppm if you took a cup and filled it with half promix/half water, let it soak overnight and check the water will be over 1000ppm. So they say to get Sunshine Mix #4 which is like the same as the promix with a much lower ppm, like 300ppm or so. Then again, tons of people on here use promix also...just sharing what I've read