I recently bought a classic soft filter.I bought a quarter of the new product.However, I purchased 1/2,1/4,1/8 from eBay.The concentration of the recently purchased 1/4 = used 1/4 is not rightA quarter of used purchases are too strong.And one-half is weaker than one-eightOne-eight is stronger than a quarter of a new product.Why is it so unbalanced?