Cleaning cobblestones from sand

I understand your problem. I clean my terrace with soft soap and a scrubber, basically everything comes off and the upper arms get trained too. Whether that helps there, no idea. Pressure washers are often not good, they roughen up the surface. At the transition from street to pavement, you also pull up the dirt every time. Just ask the manufacturer what you can use.

except as it was delivered and was on the pallets).

The supplier seems to have at least delivered the stones that look correct at first glance; unfortunately, it is no longer possible to determine whether they were of the right quality.

It is normal for concrete paving to still be setting and to look unattractive at the beginning, especially with dark paving colors.

With only shot-blasted paving, it is unfortunately also normal that dirt can settle in the pores. As has already been pointed out here several times, you unfortunately made it much worse by using a high-pressure cleaner. You have now pressed the sand used even deeper into the pores and increased the surface of the concrete.

Thus, you have also taken away the supplier’s opportunity to make improvements. Unfortunately, I do not know how to get it properly clean now without chemical agents and not have it become even dirtier afterward.

I don't know if the supplier is the same, but the stone from all the neighbors comes from a factory here in the area.

I tested the high-pressure cleaner on 5-10 stones and already saw that it doesn't help.
Then I only went over the entire yard with a spray jet. Even the joints remained intact.
So nothing should have happened yet.
Scrubbing doesn't help. I would really have to scrub so intensively that one stone takes 5 minutes.

I even ask myself with the question whether I'm stupid for asking how to remove sand from stones.
But somehow it really turns out to be difficult.

Our landscape gardener had talked to us about this beforehand,
colored concrete looks dirty and grimy over time, no matter how beautiful the catalog pictures are.
Natural stones retain their appearance for years and stay beautiful,
except for the snow-white ones, which contain lime/chalk and turn green from moss and algae.

We paved 200 sqm, which was accordingly expensive and now the stones really look like they were freshly blasted from the mountain. That’s really annoying me a lot in the initial phase after the new construction. And yes, it sounds like a square if I say that this stone was laid everywhere in our neighborhood and it looks there exactly as it should.

That certainly cost a lot of money but it is not an expensive solution. Yes, the stones look uneven. It’s OK that this annoys you and it doesn’t make you a square. Not in my eyes. What is different with the neighbors can certainly be found out, because something is different, possibly the stone itself (as already suspected) or the initial treatment or....

Pressure washers are often not good, they roughen the surface.

Pressure washers accelerate subsequent soiling. I would definitely avoid that.

Since there is hardly any chance to complain about the paving with the installer, a professional who cleans and seals gently will help you. For this there are, for example, some franchise companies that are very present on the internet and have recognized the problem of patchy pavings. Tip: If one of them comes and wants to demonstrate a sample of their skill on your paving – give them an inconspicuous stone, because otherwise you will definitely accept the order, since a super clean stone among all the other dirty ones in a prominent place will increase your pain. Also consider a certain price elasticity for your area.

If you were using "yellow" sand there, the issue is simply settled. That stuff stains like crazy, you won't get it out anymore. Too high clay content. Water washes it out, the mixture sets firmly. Concrete is open and porous, it will have soaked in. Nothing more to be done!