I would move the rock formation near the filter if it's a juwel and put some plants growing up the rocks, it just looks shoved into the back in the centre, dosn't look natural, play around with it to you find a better place.
It looks great! I will have to find somewhere to nick some slate from.... I might take a walk through the fields tomorrow. I might go through the fields on my way back from pets at home if I can remember the way.
I think your tank looks nice but will be even better once you have those real plants in it will finsh it off a treat . The slate is a nice touch and your fish look really healthy