How to assess descaling progress?

[BaristaMcBob]

I'm working on a home HX machine and do not have the opportunity to inspect the inside of the boiler. I've never descaled a machine before.

I have no idea how much limescale is built up. Can I tell by looking at the drained boiler liquid whether the boiler is now clear or whether I need to repeated the process? I'm using Urnex Bio Caf descaler.

[cafeIKE]

Can't comment on the Urnex product, but with Citric Acid, when the water runs clear, you are done.

From a long way back Simplified HX Descale [PourOver]

[BaristaBoy E61]

Can I tell by looking at the drained boiler liquid whether the boiler is now clear or whether I need to repeated the process?

When descaling using citric acid, I always take pics of each purge to evaluate progress and maintain separate pics for steam boiler and brew boiler as our machine is a double boiler. So I 'treat' the boilers separately.

The colour for the purged liquid runs from dark green when there is a lot of scale to light green to blue.

[cafeIKE]

BTW, when the water runs clear, I remove a fitting and do two flushes. It's a lot quicker than running gallons of water through to get rid of the sour taste.