I doubt you have any hydrocholic acid zones in a tank taht is five weeks old. That would be close to impossible.
Actually anoxic zones are where anaerobic bacteria live, and are what a DSB
(deep sand bed) is all about. Black areas in a DSB
is where you may have a hydrogen sulfide buildbup. They should remain undisturbed and they should dissapte over time as the DSB
From another board:
" In DSB
with little maturity and insufficient bacterial pops, black areas of sulfate reduction may develop, as well as problem areas of high mineralization of ammonia to nitrate without sufficient denitrification to reduce overall nitrate levels in the system. This may result in substrate blooms of Cyanobacteria and/or diatoms and/or dinoflagellates and/or microalgae"
So how deep is your sand bed?
And I doubt there's much bad going on in only 5 weeks.