Fertilizer can be so beneficial to succulents, but just like anything, too much of a good thing can be harmful. Many soils, like your cactus soil, already have fertilizer in them. This shouldn’t hurt your succulents if they’re larger and more established.
If your succulents are small or don’t have many roots yet, I’d recommend adding in another soil that doesn’t contain fertilizer just to be safe. Sometimes you just have to experiment and see what happens though.
When using soils with fertilizer in them already, or using slow-release formulas, the fertilizers can actually do more harm that good because they are highly concentrated and can burn your succulents. That’s why I use Haven Brand’s Manure Tea.