Yes, you can get borax there as well, but I don't remember the price. You also get baking soda at a reasonable price there. Don't buy the one from the supermarket, it's too expensive.
Yes, sure you can get potassium hydroxide (if this is this KOH)- it is just more expensive than the NaOH. The German seller sells KOH for 5,50/kg, in the pharmacy they charge around 10 Euro if I remember correctly.
Try your local pharmacy. I live in Austria (which is more or less next to you :lol: ) and here you can get NaOH powder in any pharmacy. If you pm me I can get you a German supplier who might ship NaOH to Slovenia as well.
They charge 4,90 Euros per kg.
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