Fluid H-UV is universal fluid for UV curable inks. It’s very safe for the print heads even from a long term exposure. It works best when pre-heated to 40…43C. Do not use the heater of the ultrasonic tank. The ultrasound itself will heat up the fluid. Avoid heating over 47C to prevent damaging the machine. Use the fluid cooling feature on PHD12/13 and set the max temperature to 45C. Do not leave this solution inside a print head for more than 12 hours. Flush the head out using the Intermediate Fluid or the flushing solution that came with the inks that were used on that print head.