That's a fair assessment. I'm on RO water and I can't remember if I had any PH fluctuation when I was running jack's 5-12-26 with tap water. And to be fair I've no experience with Jack's Tap formula. However, I think you're on point as rockwool being your PH culprit. I specifically use #4 perlite or hydroton, because they are truly inert. They don't affect your PH or interact with your fertilizer in any way shape or form. Rockwool and coco do not share this inert attribute which is why I never recommend either. There are simply better options that do not cause PH fluctation. Why not use them and ditch the problem mediums? I use and recommend #4 chunky perlite because it's the cheapest light weight inert medium I can find readily available all the time. It doesn't interact with my fertilizer. It doesn't interact with my PH. It is truly and inert medium. I get 1.5cu ft for $40. 2 bags is enough to pot all the plants for an entire flower cycle, and that's a 12x16 dude! The point is there are other mediums that are much better and will cause you less headaches. Hydroton isn't bad, but it's fucked up heavy and offers no superior benefits to perlite. It is also more expensive than #4 chunky perlite. Ditch the rockwool my friend. It is causing you unnecessary PH fluctuation. Switch over to something else that doesn't do that. Anything else
Found this on RW:
One of the drawbacks to using rockwool cubes is the special care and consideration that needs to be taken when working with them. While they are a beneficial resource for hydroponics growing system, they do have some important drawbacks that need to be addressed.
- DO take the time to properly prepare rockwool cubes before starting seeds or trying to root cuttings. Their natural pH is too high for optimum plant growth and will create problems and instability within the hydroponics system if left at that alkalinity.
Rockwool is a mainstay growing media for commercial hydroponics growers. I'm going to find out its use, how to prepare, and use it for growing, and propagation.
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