it is possible that your salt bucket needs to be mixed. i have had a bucket of IO reef crystals test low with Alk. IO says to mix the salt bucket as things may settle. ultimately, the outcome was still the same. a newly mixed batch tested at like 7dkh in comparison to the new bucket i just opened which tested at like 12.8 or something close. IO ended up sending me a replacement bucket for the batch that was measuring low. i would do an alk test on a freshly mixed bucket of water to see what it comes back with. it might be the reason why its low to begin with?