We've deduced after decades of experience that hot tub filter caps and pool equipment valves can be hard to turn—even for a healthy person with no serious problems. The cap or valve loosening/twisting problem becomes magnified many fold if you're talking weak, sick, injured, small, elderly or young people. Some people develop carpal tunnel or fibromyalgia or arthritis and cannot twist these caps and valves. We even found a defective valve (brand new) on our hot tub heater/filterer system that was almost unturnable by anyone's standards.
All of which leads us to a need to turn a difficult job into a snap, even for weak, sick, injured, small, elderly or young people. Enter: our own invention, the handy dandy valve and filter cap tool. Someone should patent it. Go ahead—we don't care. You have our permission. We want nothing in return. We built the tool with a one by six board and a jigsaw. We made templates by tracing around the pool valve handles and filter caps onto a piece of paper with a valve stem sized hole cut in the middle and a slit from hole to outside so we could put the paper around the stem and trace downward onto the paper. We cut out a hole in the paper the shape of the tracing for both objects. We put the templates onto the wood, traced the inside of the hole on the wood, then jigsawed them out (starting with a drilled hole the width of a jigsaw blade, obviously). The result is seen below. The main thing to remember is that it's easy to OVER-tighten, since the leverage factor is intense!

Do-It-Yourself Accessibility Wrench for Pool Filters and Valves

PVC Pool Pipe Valve

Pool Filter Top