Was fehlt meiner Pflanze?

Should I use the calmag fertilizer with every watering?

you just need to correct the deficiency it doesn't seem like a sulfur deficiency to me but more like a general lack of nutrients... I saw that you use biobizz and like everyone, you put in less than recommended, but biogrow is very light and the minimum should be what is recommended I’ve never used Epsom salts but they say they’re a miracle cure and contain magnesium and sulfur, so you can keep giving them and the calcium correction is also needed... but stop the Epsom otherwise you'll go overboard with magnesium keep in mind that the sulfur deficiency can be corrected but very slowly, so be careful not to overdo it so what you need to do is increase biogrow, do some watering with the Epsom, and then replace them with cal mag... if you can get some mycorrhizae that wouldn't be bad...