Hello all, new to the hobby, looking for some advice! I have a few wide horn hissers that I was given by a local friend, and though I've been wracking my brain to think of anything that they could be missing, they just won't seem to thrive. I've had them for about five months now, and I haven't seen any evidence of reproduction, or any oothecae. I've helped care for many insect species before, including several roaches, but I must be doing something a little differently from what these prefer. All the caresheets I've found insist that they're very easy to care for, without much more information than the basic.
I have them in a repurposed 20 gallon tall fish tank, heated by a lamp (turned off during the night, so that they can do their nocturnal thing) and a under-tank heating pad (attached to a side of the tank near the bottom, as I was nervous about putting it on underneath the tank itself, given that the tank rests on a wooden surface). Their tank stays around 80F during the day, cooled to 72-75F at night when the heat lamp is turned off. I try to keep their humidity around 40% or higher. I have them on coco coir as a substrate, with local leaflitter (frozen for a few days before being added to the tank), a few rocks to sit on, and a hollow half-log thing from the petstore (the roaches spend most of their time sitting on top of this). They also have a few plastic plants (cleaned thoroughly with a little dawn and hot water) for cover. They have a very shallow water dish with little rocks (the kind sold to increase drainage for potted plants), both lightly bleached, washed off, and air-dried before being added to the tank.
The roaches are fed a mixture of things as I desperately try to get them to show interest in something, but they always have a fruit/veggie (strawberry tops, cut-up oranges and bananas, butternut squash, broccoli, etc., though usually the strawberries and oranges) and a protein (cat food and/or generic fish flakes). I replace their food daily, and check it for evidence that they've eaten any of it. They seem to eat very little, given they they're six big roaches, and have recently dropped off from consistent nibbling to hardly touching their food at all. One of them, though they're all adults and I don't know how old they actually are, died yesterday. I've tried everything I can think of, even completely cleaning out and redoing their enclosure about a month ago, just in case they didn't like something in there.
I'm concerned about them, but for the life of me I can't find the problem. Is the temperature too low, too high? Does it vary too much? Do they want more humidity, or less? Images of their setup are attached. Help appreciated!