What grade Walnut shell needed for interior fuel tank cleaning.

[Magic]

I want to Thank everyone who recommended the Evapo Rust for inside fuel tanks. I completed my 2 tank project cleaning up the inside of the lightly coated rust from sitting many years without fuel in them. It seemed to work great and I did add Marvel Mystery Oil to the tanks for a few days rolling them around to coat the insides before mounting and adding fuel hopefully very soon. My question on the reusing the Evapo Rust, I had used 3 Gallons to fill the tanks one and a time and after doing both tanks the color of the liquid turned black and I wasn’t able to see to the bottom of the bucket I poured it all into. I would normally discard it all and wondered how much strength could possibly be left in the liquid to possibly use again on something else? It’s all back in the original 3 gallon containers but Unsure if it’s worth keeping. It only cost me around $90.00 for the 3 gallons anyway. Thank you all again. Good Stuff!