Also, that's not descaler. Those tablets remove oily coffee deposits, the brown stuff.
For descaler use Scale Away or Oust or similar from the supermarket. Scale Away is citric acid, so use supermarket stuff this time and get a 500g tub of citric acid crystals on eBay for next time.
Is there any virtue in increasing the strength of the descale solution? I’m using these
https://www.amazon.co.uk/Cleaning-Tablets-Coffee-Espresso-Machine/dp/B01N02TG8E?ref_=ast_sto_dp