Water management help in Vivarium

[LizFace]

Hello, I am a fairly new owner when it comes to tropical reptiles and snakes in general. I have a female Brazilian Rainbow Boa that is around 3 months old that I’ve had for a little over a month now. As for keeping reptiles, I’ve kept several desert lizards for many years now. As for the Boa herself, she’s been fantastic and I have no issues with her. I understand all the requirements for keeping, but the humidity itself has been troubling me. Keeping it up around the 95% level hasn’t been difficult, and she seems to be enjoying it. I have an issue with water getting stuck at the bottom of the habitat, and getting (assumably) dirty fairly quickly. I mist 2-3 times a day until everything is nearly dripping with water to ensure she’s getting the hydration she needs, but water always gets stuck at the bottom and gets everything very dirty and damp. Sometimes I’ve even noticed smaller bugs inside which are very worrying to me. I’ve ensured that the boa herself is healthy and not affected by these but I don’t want these issues to get more serious.
Right now I’m keeping her in a simple 20 gal tank with a screen top and glass sides. She has a gradient underbelly heating and an overhead ceramic heat source that gives the habitat around 80F ambient temperature. From bottom to top, I have a layer of cardboard, a reptile mat, Zoo-Med eco earth, and sphagnum moss. She has a water dish about her size, several things to climb on and a live plant.
Is there any way I should be filtering out the water besides the weekly cleaning? Is there something I’m doing wrong with the habitat itself? I want to ensure that her enclosure is safe and optimal since I really care for my reptiles. Thank you!