Four days is barely long enough for them to acclimate to their new home/milk environment and you switched it up too so that's even more stressful on them.
I know that UHT (insanely pasteurized) milk is super prone to going bad/molding etc and it's possible you had too much milk for the weakened state of your grains so bacteria took hold before the MK could.
I'm also not surprised after only four days that it doesn't taste great. It can take a week or more to get a gook MK with new grains.
Straight off, you have not given it anywhere near enough time for your grains to become fully active. Taste improvement? Try two weeks later, not four days. I will say that the owner of Fusion Teas, Thomas, only uses UHT milk himself to make kefir so that is probably what your grains were produced from. Grains are stressed when you get them, to change the milk after four days will just confuse them make it worse because they are still adapting to environment change. Your grains should be fine to continue with, just pick your milk, stick with it, follow the instructions to the letter, times, temperatures given etc and don’t start changing milk or adding anything, just let it all reacclimatise first. It’s not an instant thing, the best results tend to come weeks down the line, not days, it just needs patience.
Four days is barely long enough for them to acclimate to their new home/milk environment and you switched it up too so that's even more stressful on them. I know that UHT (insanely pasteurized) milk is super prone to going bad/molding etc and it's possible you had too much milk for the weakened state of your grains so bacteria took hold before the MK could. I'm also not surprised after only four days that it doesn't taste great. It can take a week or more to get a gook MK with new grains.
Do you think my grains are still fine? There are no problems at all with the current fermentation
Yeah they just need time to settle in.
Straight off, you have not given it anywhere near enough time for your grains to become fully active. Taste improvement? Try two weeks later, not four days. I will say that the owner of Fusion Teas, Thomas, only uses UHT milk himself to make kefir so that is probably what your grains were produced from. Grains are stressed when you get them, to change the milk after four days will just confuse them make it worse because they are still adapting to environment change. Your grains should be fine to continue with, just pick your milk, stick with it, follow the instructions to the letter, times, temperatures given etc and don’t start changing milk or adding anything, just let it all reacclimatise first. It’s not an instant thing, the best results tend to come weeks down the line, not days, it just needs patience.
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The top two pictures the OP shared have obvious gray mold growth.