For one, your temperature is way too warm for dojo loaches.
Did you acclimate yours to your tank's water conditions before putting them in? If you put them straight into your tank, the difference between your water and the store's water where you got them from could have been drastic enough to shock their systems.
I suggest you get a good test kit, either the API master freshwater test kit, or the Hagen kit put out under the name of Nutrafin.
Dojos are usually pretty hearty, so if yours died after only four days, they were either sick to begin with, shocked by water conditions they weren't acclimated to, or made ill by poor water quality.
If you decide to keep them in the future, you should keep them in cooler water, no warmer than 70F, maximum.
-- bigmamafish