The video is very good, had seen it some time ago.
Just like bathrooms getting mold around the tub from too much humidity, your wet palette responds the same.
Use of distilled water helps. Real copper in the form of old (not the modern alloys to look like copper) coins or wire under the sponge. Some of the venders sell copper shaped pieces to hold your paper from curling as it dries. You will need to thoroughly clean your container and sponge to start over.
I have tried a small amount of H2O2 (hydrogen peroxide) to the water as it is a gentle bleach. You should not need much. I originally tried just using the 3% version, sold in our supermarkets and pharmacies over the counter, and found over time the top paper began to break down. Did not find any affect on paint using the 3% only. You would just need enough to keep the mold from forming. H2O2 's strength diminishes quickly once the bottle is opened.
If you paint infrequently, a closed wet pallet will develop mold over time. Some friends use a new paper towel or tissue and a new parchment paper almost every painting session. Basically a disposable wet palette.
I reviewed the video and be aware that not all parchment paper is the same! Some seem to have a different coating than others. Even though the tape says unwaxed parchment I know someone that uses, what we call wax paper in the US, to great success. So some experimenting is required on your part. There is the Masterson Palette in the art stores that I know people swear by the paper. They buy the large size replacement sheets and cut them down to size needed.
Your adventure continues!
