River rock or washed gravel is a lot harder to walk in compared to 2-4" limestone. The gravel wants to roll when you step on it especially on a slope. The limestone will also very slowly add some lime to the water; not a lot but measurable. The pros of gravel is it usually grows less algae on it compared to lime stone. Lime stone especially the lighter colored softer types, leaches calcium carbonate and some phosphoric acid, both used by algae for growth.
As usual there are pros and cons.
I can attest to the algae liking the crushed limestone. If the water level rises a few inches, within a couple days there is a bright green covering on the newly water covered area of the rocks and the snails are on this new band of algae like white on rice. Snails seem to love the new growth. The growth just below it will be of a darker color.
I ought to have well fed RES, because I have snails by the gazillions.
