Need epoxy or other sealer

Perhaps if you ditch the pea gravel for leveling sand you won't have this issue. Another thought would be to fill the holes w Quik Crete almost to the top and then mix the pea gravel w concrete to top off.

OR....how about pouring in stained concrete to retain the look of differentiation?

Not exactly sure what to suggest, but just wanted to say, you did a great job, love the look! 👍

Is this the kind of product you're looking for? https://www.aeromarineproducts.com/product/aeromarine-rock-pebble-paving-epoxy/

There are directions here for prep and application on a patio, though I expect steps would work the same way: http://www.doityourself.com/stry/how-to-coat-over-a-pea-gravel-patio

I somewhat agree with Robyn Garner's idea of filling the blocks with concrete. But....fill the whole blocks with concrete even with the surface. Then as it begins to set up, embed the pea gravel into the surface. Use a damp sponge and wipe the concrete away revealing the pea gravel. Concrete finishers use a similar process of embedding pea gravel in concrete walks. As the concrete begins to set up, they use a garden hose and wash the surface concrete away revealing the pea gravel. A lot of older concrete walks were done this way.

Looks great .... here's what you need.... https://www.youtube.com/watch?v=wobZEu8KaPY

I LOVE your steps.........Unique and clever idea.........I see they make boot trays, with pea stones for in the house and pour something over them, maybe you could check out that?

will plants grow up from it