Hi there,

Indeed the CRR (constant reserve ratio) is a fundamental part of the Bancor protocol and Smart Token functionality. Because its percentage is held constant to the total Smart Token value (supply x unit price), its can only “bleed” to 0 when the very last Smart Token is liquidated (meaning that the total supply would be zero, thus also the reserve amount.) The reserve balance itself will fluctuate with buys and sells but its proportion to the total will be fixed. We published an article on our blog explaining the fundamentals of Smart Tokens. Please check it out and let us know if you find it useful: https://blog.bancor.network/smart-tokens-101-63edc2cc5a89