How to clean pool main drain

[russvacant]

Very new to this.

I have tried vinegar to clean it, a pomice stone, baking soda. Then i moved onto the chemicals, muriatic acid and used a watering can to place directly on the sides with a 1:10 part water ratio. Increased it to 5:10 ratio and nothing is moving, with a wire brush.

Has anyone had this problem, if so, is there an easier solution;

Thank you in advance.

https://drive.google.com/open?id=1RNT8qXElfHwsFjnlVSnV_2RpPrVUIDOv

[Teapot]

I wonder what that mess is, never seen one as dirty as that. Can you dig/scrape a bit off?

[Denniswiseman]

Have you tried neat muriatic acid directly on to it