I should start by introducing myself. I am Vicki. I have a 45 gl tank with Metal Halide and atinic? lights. They are supposed to be high enough intencity for any coral I want to grow. I am presently wondering why a rock I got at one store has changed from mostly gray to mostly whitish green and kind of chalky looking, while my other rocks from a different store have the rosey coraline and a little green algie that was there when I bought it. There is also a round grapelike growth on one of the nice rocks. Is that a good thing or a bad thing? I did put some calcium powder in the penguin filter I have on the back of the tank rather than right into to tank and I am wondering if that could have fallen down to this rock in question that is right below the Penguin outlet lip. It doesn't make sense that one rock is odd while the others are doing great.