Low SE & E


I am wondering if anyone else has come across this problem. the horse is being fed Uckele's E& Se , plus Lodi's Super E.But both my sel & E levels are low. They get netted grass hay 24/7 .electrollytes, Mg. I am doing something wrong. Also SEL -E 10 cc shots May, another 5 cc middle of july.

What could be the reason for the E and SE to continue to be low?  would too much iron do this? the hay was tested last year but new hay has not yet. thanks