Ok, I have an issue. In the brinsea mini, a tiny bit of water equals a LOT of humidity. But I guess that does not stand true for the 20. I do not have the humidity pump. I filled one reservoir has high as I could go without spilling over. Humidity just hitting 30%. So I added a little water in the other well, I'm around 35% now. I have 2 calibrated hygrometers in there. So I guess I need to fill the whole other side. I want to be around 45-50% humidity. Lockdown will be a nightmare! But we'll cross that road in two weeks. So should I just fill both as high as I can?
Humidity comes from the surface area of the water, not the depth. So you might want to try cut sponges in the other channel so you can add or subtract sponge pieces until your humidity gets stable.
The air in your house might be really dry this time of year due to running your furnace.