Did you ever get the Unicel replacement cartridges? The sort of iron precipitate I'm seeing in your buckets should be filterable. If you use the Unicels + polyquat (both an algaecide AND a clarifier) + HEDP each time you fill, you may be able to work out continuous control, with no cloudy or brown periods.

It will probably take some experimentation and testing on your part to get it just right. PLEASE do tell us what works and doesn't, so others can benefit.

And, the mini-pool idea, if you want to try it, will allow you to fill with mostly iron free water. Essentially, you just do a 'bucket' test in a 500 - 1,000 gallon pool, let everything settle, and then hang a small sump pump above the sludge, and let it pump the clear water into your pool. However, rather than adding bleach + soda ash, I'd use bleach + borax, so you don't end up with really high TA in your pool.