What kind of soil is it? It sounds like a very dry peat, that once dry it's hard to re-wet (hydrophobic).
Just wondering, sorry I can't help - I never used any wetting agents.
Rina

I have to agree with Rina, sounds like peat. I've never encountered your problem using a gritty mix. I've seen and rescued a lot of plants with that type of brick or concrete-like soil. It's very hard to hydrate. The first part of the rescue is to soak the entire plant...sometimes while it's still in the pot, in warm water and even then it's a real chore. The roots may be quite brittle so the warm soak helps with removing the dried soil from it.

When my peaty soil wouldn't rehydrate, I put a bit of water on the top and wait until that absorbed. Then watered fully. Takes time but worked. Spray bottle helps too.

Agreed with Neil that the best solution is moving to a different or modified soil mix.

I still run into that with potted tomato plants, where I still find a use for peat. I submerge the pot into a tub of water and keep it there until air stops bubbling out of the soil.

ez

It is a comercial cactus mix or whatever they came in when I bought them. It looks like there is some peat in it. The ones I have in a gritty mix seem to suffer the most. It probably would help if I got them all into the same soil mix.