in my case, i have the rommels red acro, 2 years + only incrusting a couple of mm, and my DFS pink panther acro along this years not incusting not nothing only stay ( thanks God ). i have the Purple Monster and the Oregon tort, i`ve seen the slow growth, but it do it. My Rommels red was two years doing nothing only encrusted a couple of mm and fattened a little, i just a couple of weeks before change it base and at this days it start to encrust notoriusly like never before.
