What kind of algae eater? I have golden Chinese algae eaters & I had one that disappeared on me. I took all the caves out, shaking them as I went & set them on the table. One CAE
was still in the tank but the other - GONE! I went back to the caves, shook & gently knocked on the one, he had suctioned himself to the inside & would NOT come out. He was out of the water about 15 minutes. To this day he will hide in his cave & is a bugger to get out when I want to re-arrange things. Sorry for the long story. Bottom line of you any decor he can get up inside that's where he could be.