Hey Howie, I know EXACTLY how you feel. I went through something extremely similar (almost identical) to you earlier this season. I will post the link to my GLog at the end, and you can get more in depth, but here are the cliff notes.
I was running a 600w dimmable MH at 75%, Hoffman's seed mix, temps at about 82-85 F, and fans/CFM to keep the air flowing. I cursed the lights, and changed em, I cursed the soil, and changed it, I cursed the fans, and changed em, I cursed the water and let it sit in buckets to get rid of nasties, and in the end I feel it was a combo of Soil and watering (with the watering being the main issue I was having). I was bottom watering and adding about an inch and a half of water in the bottom of the tray and letting the soil soak it all up. This was what killed me. It turned the Hoffman's into mud and killed about 150 seedlings. I switched the soil to PROMIX, and began to top water with very little water, a good squirt per cell every few days (when the tray is super light). This fixed my problem. Just for good measure, I planted a dozen or so seeds in Hoffman's the second go around to compare it to the promix, and they all survived, but they did end up growing slower.
In the end, I was killing them with the water. I thought that an inch of water (even when it was light and dry) was too much. I found out that it is better to water every other day or so, albeit a much smaller amount, than to go with the ease of bottom watering (for me). In the end, everything survived (after the initial and subsequent hundreds of dead) and in the future I will probably go with a different mix than Hoffman's and water from the top. I know that there are a number of very reputable and amazing growers that swear by Hoffman's, and that is testament to its ability to really produce for you. But I just had problems, and instead of trying again I am gonna stick with something that worked for me.
Here is my
GLOG and pages 3-8ish covers the Death and Carnage!
