I am in the UK, I have been doing exactly the same as you, I recommend feeding the Stendker goodheart beefheart a couple of times a day, the best advice I can give you is feed and water changes, I would do 30-40% every other day if you can, it stimulates the growth, I use a HMA filter for water changes, with good feeding and frequent water changes, keep them warm they will colour and grow better, less chance of a stunted Discus…Good luck.
https://aquariumscience.org/index.php/7-filter-media/
This website has saved me a fortune I have a filter full of pot scrubbers and a filter full of 30ppi foam from Swiss Tropical I had it shipped over, have a read through all the chapters it is brilliant advice.