I will try not be sound too aggressive with this...I think when people post that clams can be kept under PC, it is a mistake because of misinterpretations like yours. You are offering essentially 110 watts of "usable" light to a clams at 22". The two 55 watt actinics will provide little to no usable light, particularly at that depth. This is GROSSLY unnacceptable in my mind. I feel; your clam will die from light deprivation. If you had a crocea under these conditions, you were tempting fate even further. Crocea are the most light loving clams, and will fail under all but the most intense lighting, of which PC is far from. Furthermore, a month is far from an indicator of success. Clams CAN be kept under PC, just A LOT of PC, and at a very shallow depth. But people dont hear this, they just hear, "Oh, I can keep clams with PC". There is my objection. It is just my opinion, take it with a grain of salt.
I hope I didn't sound too "my $hit dont stink", but this topic seems to keep rolling around over and over.