Sponge rock is perlite, just a larger grade. It seems that the largest available now is #3...I always liked the larger #4, but that seems to be unavailable now. I have used CHC for years...I am now switching many paphs back to bark...to many problems with CHC lately,,,yellow leaves, and roots only at the to of the mix..and yes, I do soak CHC a minimum of 3 times, using Ca N03 and MgSO4 the second soak....regardless, bark or CHC needs a very large amount of aeration...sponge rock, lava rock, diatomite...anything. Take care, Eric Muehlbauer in rainy but mild Queens NY....paphs philipinense, hookerae, and venustum in bud.......
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