I've been noticing these black spots on my pike for the past few days. I got a little green terror had it one night and found it dead with the same black spot covering its entire head (the pike had started to get it before the green terror came). The pike is the only fish that has it. I checked my parameters everything is fine but my nitrates are alittle high. Around .40 ppm I have been doing 25-50% water changes every 2-3 days to help with the nitrates spike. What can this be? 
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