Did you shorten the photoperiod after switching to MH? It's too much of a shock for the anenomes probably.
What species of clams do you have? If you've got croceas or even maximas, then the general rule is 250w+ MH is almost a must for these 2 species. These are light intensity loving species. IMO, T5's won't get them coloured up to their potential and might even starve a crocea. Squamosa, Derasa are probably fine with HO fluroescents however.
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George
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