Quaternary ammonium salts should not be directly blended with anionic surfactants (as charge neutralization occurs, leading to inactivation). Compatibility requires bridging via nonionic surfactants (e.g., fatty alcohol ethers). Avoid mixing with strong acids (pH < 2) or strong oxidizing agents (e.g., sodium hypochlorite) to prevent decomposition and reduced activity. Blending with nonionic or amphoteric surfactants enhances synergistic effects and improves overall performance.