I haven't got reply yet from Boyd,but got home and read labels for VitaChem, Hikari sticks and tetra crisps. All have Thiamine Mononitrate listed in ingredients.
Looking at Mr. Internet, for humans appears too much thiamine is not a worry. Did you know that B1 deficiency causes beriberi?
Here is a story about of thiaminase problem with a snake. Appears that to get the B1 into the body thiaminase rich foods are not good every day. So as far as the minnows go if I can tone em down and feed good foods + Boyd, should be ok.