The pea gravel is of various sizes and shapes as well as a variety of textures some small peices being a little coarse and the largest 1/4 inch being not so course. i wouldnt say my firemouth is a digger seeing as he spends most of his time in his cave except for when im out of sight or gone from the room. i thought of adding the smaller of my acaras a day or two later after the layout of rocks and wood is done and the firemouths settled in. would it be ok to add him now and then check on the ph in a few days?