Thought some might be interested in how much scale you can expect after 3 years with, what I thought, was good water conditioning.

I used RO plus TWW exclusively in my Pro500 PID (bought June 2018 .. so 2 mo. shy of 3 years). The RO from a local store was a new installation and I've measured the TDS over 3 years and it never is above 10. I use the espresso blend of TWW exclusively with 5 gal jugs. A few days ago my steam pressure gauge stopped working and after reading posts, thought it likely due to scale, so I cleaned my mushroom today. The pics are below. The mushroom cleaned reasonably well with solution, but the chrome on mushroom tube bubbled and came off in spots.

Because of the way the gauge is installed, I could not remove the steam pipe tube to the gauge. I removed some wires, but not the entire boiler .. and it was in a difficult place to get at.. Thought I'd break something judging by the force I was using. All I ended up doing is rotating it on the face.. which I only recognized after it was all put back together.. (not a great way it was installed.. the gauge rotates as you try to remove the nut and almost impossible to hold the gauge with the little access I had) So no steam gauge.. but I don't use it anyway.

Others can comment as to how much scale that is.. but likely if I'd gone with RO and Potassium BiCarb, I might have less scale. I'm not sure if the scale could be attributed to the small amount of impurities in the RO or is all due to TWW.. so don't want to blame TWW for scale.. but it appears that TWW is not totally scale free.

Likely I should descale the boiler.. but that is a huge amount of work.. not sure I will tear it all apart to do.. as I'm finding the Robot does as good a job on pure espresso.

As a contrast, here's a recent post from someone who used RPavlis exclusively for two years.

This is what two years of RPavlis water looks like

This post got the better of me, and convinced me to pull my mushroom to confirm that using RPavlis was working as I expected (hoped?). After 16-17 months of daily (or twice daily) use on my HX, the mushroom looks brand new, just like the one Auctor linked to. So, one more data point in the favor of the RPavlis recipe. I also use the standard recipe [distilled + potassium bicarb].

Maybe an expert can weigh in, but I remember reading from RPavlis's old posts that he advocated for descaling a machine by running pure distilled through it for a period of time (maybe on the order of weeks-months). I think the idea was that by absence of any mineral content, it would slowly dissolve the scale, and presumably not be corrosive due to the mineral content it picked up. It sounded like a gentle way to descale a machine that wasn't suffering from major problems, but don't take my word for it. Read the RPavlis posts yourself and proceed at your own risk.

Wow, what was the tds of the water after adding the mineral packet? Did you ever test the ph of the water from the store?

Auctor wrote:As a contrast, here's a recent post from someone who used RPavlis exclusively for two years.

This is what two years of RPavlis water looks like

Wow.. yes.. that is nice .. thought I'd get that from TWW... Distilled is hard to get where I am.. they only sell in 4L bottles and anything less than 5 gal is too much lugging.. But if I were doing it again.. I'd use Potassium BiCarb

SCespresso wrote:Wow, what was the tds of the water after adding the mineral packet? Did you ever test the ph of the water from the store?

TDS before TWW was 5-10.. after adding and a day to integrate was about 120-150. I never tested the ph from the store since the TDS was so low, just assumed it was pretty neutral.

Bluenoser wrote:Distilled is hard to get where I am..

I hated lugging around the gallons of distilled, and the thought of all that wasted plastic bothered me, so I switched with Zero Water + Potassium Bicarbonate. Four months in and it's a relatively easy workflow (admittedly, I only make 3 shots/caps per day).

Since I got a "Robot" I found that the espresso is as good if not better than the HX.. and I find I sink fewer shots. Even with a really good grinder, as the beans age, the shots can change a lot from day to day.. With the Robot, you can adjust for that by reducing or increasing pressure. I'm really rethinking whether I'd get another electric/pump machine. Can use any water, no flushing of steam boiler, no chem clean, no back flush, .. no replacing parts that fail (had an SSR go) . I was pretty religious with this machine.. but likely I won't get more than 4 years out of it before the boiler needs a major descale and a pump replacement.. at that point, I'd look for an eager new enthusiast with lots of tools.. .

Which TWW formula was this?

I'm late replying, but I think in light of other recent discussions about TWW and 'scale' that I'd weigh in with an opinion FWIW.

I agree that Dave's (Bluenoser) images in that first post look pretty bad, but they look to me more like copper corrosion rather than anything we typically call scale. Limescale (calcium carbonate) would leave a whitish coating, as would gypsum (calcium sulfate). Brass and copper corrosion might leave behind blue-green coatings or blobs of copper chloride, sulfate, or carbonate, similar to what I think I see in those pictures. Acidic water, along with oxygen or especially chloride are the usual causes of brass and copper corrosion, although it can be very complex and hard to predict. Sulfate (which is in TWW as well as the Barista Hustle and other recipes) might also contribute to corrosion risk.

P.S.
While I'm at it I'll also point out that the two squeaky clean mushroom images we saw posted and linked here as examples of rpavlis water are both of stainless steel mushrooms rather than the plated brass mushrooms that are known for being a scale magnet, and for developing spots or blobs of green corrosion where the plating has flaked off. I'm a fan of R Pavlis style water for avoiding scale and corrosion, but comparing stainless mushrooms to brass plated mushrooms may not be a fair example.