HP 23 refill problem

[bigben2525]

Hello I am a new retail inkjet refilling business. I just refilled a HP 23 color cartridge about a week ago. It appeared to test and fill perfectly. However about 3 days later the customer brought the cartridge in and said the yellow stopped working. I looked at the printhead and noticed a crusty substance only on the yellow part of the print nozzle. I wiped it off and it started printing yellow again. Just a few days later the same thing happened again. I did not know exactly what to do so I centrifuged the cartridge twice refilled it and asked the customer to try it again. This was just today so I dont know if it worked or not. Has anyone had any experience with this type of problem? Fixes? Solutions? Causes? I am using the Ink Jet Factory from SME and their ink. Thank you in advance.

Ben