Digital BW, The Print

I reciently swithced from the old original Piezo ink to the PT 
Selenium. I did a flush with the original flush carts and plenty of 
purge prints. I have had a problem since installing the ink. After 
every print job, I have to do a nozzle cleaning. I can print one 21 
stepwedge and then do a nozzle check and its bad. One cleaning cycle 
clears it up, but after the next print it re-occures. The printer is 
an Epson 3000 and has a brand new black nozzle head that was 
installed just before the new inkset. The black nozzle seemes to 
check bad more often than the others but still the other nozzles 
check bad along with the black a lot of the time. 
Thank you Wilfred.