How do you clean DE filter with muriatic acid?

There is no reason to use muriatic acid to clean a DE filter. If you disassemble the filter and clean each grid thoroughly with a hose nozzle, they will be clean enough. In the case of heavy minerals in the pool water, or long periods of time since last clean, the white fabric may be somewhat discolored. Don't worry though. That's not a problem. But be sure and take the time to examine each grid for tears/breaks. Replace any damaged grids found. I'm always happy to answer pool-related questions. Contact me at anjeli-klean.com