Seamaiden hit the nail on the head. You can definitely do it. Just gotta treat it correctly. Would I do it? Probably not.
Promix HP is already blended to perfection, and 100%coco is perfect as well. They both act a bit different. Mixing them together would require more guess work(how much should I let this dry out? What pH is ideal? Will there be more or less salt build up? Do i need more
Calmag because of the coco, or does the
promix have enough in it already?) Too many questions for my taste, but it can definitely be done no doubt.
I personally love coco coir and that's all I use inside. If you're willing to experiment I would suggest throwing a plant in just 100% coco and comparing it to a plant in just 100%
promix to figure out which medium suits you better. Coco does work well as an amendment to help keep soils from becoming too compact, but it truly shines when it stands alone. No perlite, no nothing. Just coco.
Coco Benefits:
- Holds lots of air
- Doesn't compact
- Doesn't require a wetting agent
- Hard to over water
- Can be purchased in light easy to carry compressed bricks
General coco guideline:
- Never water with pure R/O(always at least .2EC(100ppm) to maintain the cation balance)
- Always pH 5.7-6.0(I like 5.8)
- Don't let it dry out or else that's a deal breaker and you'll run into tons of issues(this is hydroponics)
- smaller containers are often better when growing in coco(the more often you water the more often you bring fresh oxygen and balanced nutrients into the medium)
Here's a plant in just coco. Loves it!
Can you tell I love coco?:D