clogged heat exchanger

sw18x

<span style="font-size:12pt">I’m installing some insulated lines from my outdoor wood furnace into a SuperStor Ultra 60 gallon indirect fired hot water tank which serves as a heat exchanger for the baseboard heat in the house. I got the old lines off the inlet/outlet for the heat exchanger on the tank, and noticed a ridiculous amount of black build up (lime?) inside the heat exchanger (my index finger barely fit inside the 1” outlet). The tank is 10 – 12 years old, the owners manual for the tank says the heat exchanger coil is cupronickel. I’d really like to flush it if that’s feasible. What could I safely flush through that type of alloy that would still remove the deposits? I still have the old pex lines and the old pump from the wood burner handy so it would be a quick set up for the flush as long as the pex can withstand whatever solution I use, at least for the duration of the flush. Any advice would be greatly appreciated. </span>