Would Kribs work in my tank?

I would slow down on adding fish for a while. Yes, Biospira really helps, but you still need to let the tank settle in.

As for the elaphant nose--these are sensitive fish, and need to be acclimated to tank conditions carefully. Do some research on any new potential fish--you already have a mix that may cause problems down the road, especially once fish hit their mature size. Kribs will cause problems--they will likely breed, and make the tank a war zone. The angels may cause the same problems. Long term, you may need to remove some of them.

You could add a bristlenose eventually--not only will it help with any algae, but they like caves to hide in, as well.

What are your readings?

Yes for sure you need to slow down on adding those fish. Likely the reason that your elephant nose died is due to adding to many fish too a new tank too fast. You want to give your beneficial bacteria bed some time to form and if you throw too many fish into the tank at once that bed will not be fully formed and the ammonia and other contaminants caused by fish waste, food, etc. will just be too much for your tank to handle.

I would wait till the tank had been up and running for one month before adding any more fish. As far as Kirbensises are concerned they are number one a Cichlid, that means normally two things, they are hardy and aggressive. Now Kribs are not quite as aggressive as most cichilds but if you buy a pair they will breed and once they do they become very territorial. Considering your set up with the fish you have chosen you might wanna consider Rams over Kribs.