I say this from experience and b/c I pulled out the last MTS today.
Give it time. . .they have been known to live in bags of unused, unsubmersed substrate for up to a year; extremely hardy and near impossible to get rid of in my opinion unless you gave the tank a copper bath which is obviously out of the question. . .
Great tank and great thinking on the photoperiod and dosing to get rid of the algae!!!