If you put water in there that is ph 8.0, the prom-mix stabilizing agents are going to bring it all the way down to 5.7 ????? No way.
Yes way... I've been using Promix HP for 3 years and I have yet to put any kind of solution into it that hasn't come out within 5.8 - 6.2 range. (Haven't tried as high as 8.0 yet, but 7.5 has never given me any problems.)

How are you measuring the pH, with a meter? Is it properly callibrated everytime you use it?

Promix is a "soiless" medium and the pH range should be kept at around 5.8-6.0. And, yes, in most situations you don't have to bother with the pH (EC is a must in any situation though). Though if you really are reading runoff in the high to mid 6's then you should definitely try pH downing (obviosly try one plant first.)
Believe me, as helpful as these (and similar) forums are there seems to be a general lack of understanding of Pro-mix and related media.



I have had problems of my own recently that sound very similar to those that you are describing: yellowing and burning leaves that seem to come around week 6-7 in the plants life. I have yet to pinpoint the problem exactly, but here are my conclusions so far after 4-5 crops with the same problem :

1. Originally thought that it was just nute burn, but I've gone down to a 1/4 of my orignal doses (different crops) without improvement. In fact the latest batch now have many definite signs of nute def.

2. Investigated the pH possibility but have always found my pH in the correct range.

3. Have tried monitoring EC levels, and have mostly maintained those in and around what is considered optimal for weed. Though as I said nute doses were lowered so the EC has been kept lower for the latest batch. Doesn't seem to be the problem either, though I definitely have to work with this more.

Given the above I've gone right back to the source and re-looked at my tap water. I've noticed this winter that the pH has crept up from the usual 7.0 - 7.2 range to about 7.3 - 7.4. Like I said, with Promix pH should not be an issue, but this definitely indicates that something in the water has been changing, most likely the mineral content. Given that I'm constantly scraping calcium deposits off my humidifier I'm fairly certain that my water has increased in Ca over this winter.

I did some research into Ca and found that too much Ca can lock out (magnesium) Mg. I then compared my symptoms to Mg def and they seem to be a perfect match. This is a fairly recent conclusion so I have yet to test it. You mentioned that the pH of your water is around 7.3, maybe you are having similar problems? If not Mg than perhaps you have too much of some other mineral? I know that too much Ca affects Fe (Iron) uptake as well.


Anyways here some tips for Pro-mix; I've had great success with it before (using GH FloraNova series):

1. Soak it everytime you water, feed or no feed. You should aim for about 25% run off.

2. Fert salts can build up quickly in it so once you get to bud, leach with plain water every other watering for sure.

3. Don't use ferts when transplanting them to larger pots. Transplant then give straight water; feed next time (and then alternate if in bloom).


Would attach some pics of my symptoms, but can't figure it out in this forum yet.
cjus44 Reviewed by cjus44 on . Need help with nutrient lockout Hope somebody can clear this up for me. I am almost 100% that I have nutrient lockout and that it is being caused by a ph problem. Sorry I don't have any pics to show, but from what I've seen and read, I am sure it is a nutrient lockout. I have 8 plants. 3 of them have burnt tips and edges and turning yellow. 2 of them show an Iron deficiency, and the other 3 look very healthy. The medium I am using is Promix. I water with regular tap water, the ph on the tap water is 7.2 to 7.3. This Rating: 5