Everyone's got em if you have a well. Tried 2 different solutions. A "professional" solution called F9 Barc concrete restore found online and goof off rust remover at the big orange store. The F9 Barc is around $45 a gallon and is diluted at a 2:1 ratio of 1 gallon F9 and 1/2 gallon water. So $45 for a 1 1/2 gallons of rust remover solution. Goof Off Rust remover is at $10 a gallon with no mixture. Comparing the 2 against a painted wood fence, concrete and stucco guess which one came out on top? The pro stuff right? Wrong. Goof Off wins this battle as a better solution which cleans all these surfaces better and quicker along with being over 50% cheaper. So, don't waste your money and get the cheaper and BETTER stuff! The F9 MSDS has a hidden solution which they only give to your physician should you get sick. Should have been my first guess. When spraying always wear a respirator and protective glasses otherwise have fun with acid in your eyes and lungs.... Chemical information below:

Goof Off MSDS
Hazardous Components (Chemical Name)

1. Oxalic acid {Ethanedioic acid} | CAS# 144-62-7 | Concentration <10.0 % | OSHA PEL 1 mg/mg3 | ACGIH TWA 1 mg/m3

2. Hydrogen fluoride {Hydrofluoric acid; Flouric acid} | CAS# 7664-39-3 | Concentration <0.5% | OSHA PEL 3 ppm | ACGIH TWA No data

F9 MSDS
Hazardous Ingredients (specific)

1. The precise composition of this product is proprietary information. A more complete disclouse will be provided to a physician in the event of a medical emergency

2. Ammonium Hydrogen Diflouride | CAS# 1341-49-7 | Concentration 1-5%

3. Phosphoric Acid | CAS# 7664-38-2 | Concentration 1-8%