I gotta get in on this man. 600W HPS 4'x4'x7' tent with four 5 gallon hempy buckets. I have a lava rock reservoir with a coco/perlite mix above that. I personally hate the coco and will go back to 100% perlite for my next cycle. When I'm growing hydro I do want my medium to be completely inert. Coco has some odd physiological interactions with fertilizer that I don't get with perlite. Also, I find that perlite accelerates the wet / dry cycle frequency which accelerates growth rates that far surpass a coco / perlite mix. Some people seem to love the coco. As the saying goes, different strokes for different folks. Anyhow...
just wanted to give newbs/rookies a reality not really understood by you. first hempy bucket realities and options. designed to be simple and productive etc hempy chose medium of perlite and vermiculite for a reason. = the shit works with no issues. fast forward to bright ideas using a hempy. in this case with coco and perlite. many have used coco and perlite but cococoir doesn't make the best match in a hempy bucket because coco doesn't marry well with it naturally in a hempy bucket.
since you mentioned issues concrning nute issues using it but also speak on inert qualities of perlite I would say coco growing like most have found is simple once dialed in. i can't tell you why doing it in a hempy causes issues for you because it shouldn't. may be it's the size perlite you are using or some other factor i don't realize.
with that said as soon as folks started using hempy's with all manner of medium combo's many found they complicated a KISS system. some found a alternate/option that worked for them while other floundered and either gave up or had sinse enough to go back to the standard medium hempy used.
I've used the standard hempy method in a two bucket trial to test it out. i did well with one bucket not so good because i hadn't quite dialed in how to add the clone properly . totally on me but the other worked as it should so i considered it a viable method from personal experience and not just others doing it. during the same period i also started my first coco coir use. brick medium old style i had to hydrate and rinse forever. Yet, it worked and i saw the most beautiful roots in person and that sold me on coco. i have coco coir waiting for a real run now after i run the biobizz because of circumstances.
using coco with stuff like promix and the rest can also be problematic and give you funky grow results. particularly using pro mix bx like i did because it holds water longer. pro mix and perlite never and issue though. so it's based on how these mediums work together or not based on their own unique qualities.
moral to the story is simple. if using a hempy and it's working as designed let it be and be thankful.