Humidity control 75gal tank

I'm having trouble keeping the humidity in my tank where I want it. It sits at about 30 which is way too low. I have tried multiple misting's a day and with in a few hours is right back at 30. I recently started trying tin foil over the tank lid but it doesn't work as well as I was hoping. I've only had my ball for for 3 months and her health had improved a lot since I've been taking care of her but I'd like her to have ideal conditions if I can. Any suggestions or advice to regulate (mostly rise) the humidity in a 75gal tank?

Use Glad Press n Seal instead of aluminum foil on the top. You can also put a damp washcloth under the Press n Seal.

What are you using for substrate?

I have tried using damp wash clothes/ kitchen sized towels and that didn't seem to work that well either. I use lights over my lid so i worry the plastic wrap might get too hot that close to the lights.

I'm using aspen shavings right now. I was considering switching to coconut husk because it seems like it would hold the moisture better but I haven't heard much about how well it works.

Switch to coco husk and you also run a heat lamp in order to facilitate easier humidity in such a large tank. I have 2 boas each in a 40 and with two mist of a spray bottle increase it 15%. I also have a piece of corrugated plastic (think Lowe's garage sale signs) and then covered with tin foil and aluminum tape. It allows removal and installation to be easier. Let me know if you need pics...

Have you thought of maybe switching the lights out for a under tank heater?...it would keep the substrate from drying out so fast b/c the over head lights I've noticed tend to dry things out and in my opinion are best for dryer climates like lizards and such

If you want ideal conditions it'd probably be best to switch to a reptile cage. Aquarium tanks are notorious for being difficult to manage. Vision, Animal Plastics, Barrs, and Boaphile are a few sites that sell good enclosures.