TCA 15% peel on buttocks day 10 no flaking skin very dark -- should I try a stronger peel?

It is too early for the peeling to  occur on the buttocks. Give it another week or so and use some exfoliating cream or retin A to help it peel off.

This sounds like hyperpigmentation. Hyperpigmentation can be improved with a combination of lasers, Aerolase, microneedling/prp, skin lightening, peels, and skin care. Sun protection is essential. I recommend getting a formal evaluation with a cosmetic dermatologist. Best, Dr. Emer

Please perform TCA safely as this peel can cause serious burns, especially off the face. For this concentration on your body, it may take a few extra days to peel. The fact that your skin has turned dark means that a chemical reaction has occurred- this means it takes time to see the results of peeling. Be patient and go slowly with your peeling. All the best and wishing you safe peeling,  Dr Isobel Walker. Brisbane Australia. 

I can see you are an expert on peels, however as Dr Hansen has eluded, wait another week or so. As you know TCA peels depends on the prep, TCA concentration, as well as the technique- this includes the pre prep e.g.. with acetone or retinoids, the pressure, and multi- coating, additionally post peels care as discusses can accelerate peeling. All the best, Dr Davin Lim