Digital BW, The Print

I just started doing B/W.  I have a new (about 3 months) 1280 that I have UT2 inks with 
carts I fill with bulk inks. they are not put in right away but sit in sealed containers for a 
least a week. The light magenta position has has been having clogged nozzles on a daily 
basis and is increasingly hard to clear. Clean three times- nozzle check and run a purging 
test pattern. It seems to help to put a full cart. I get it back but it's getting expensive and 
more difficult, It is only that position, the others  are good. I run a nozzle check almost 
every day. Thans Kelly