Thank you for all of the information. If a gas bubble was the problem, he seems to be doing well now. He is still a different color, and yes, the "spasms" were exactly as you described. There were also some side to side moves that were happening this morning (after we noticed the color change), but he is able to swim upright, eating well, and even anchored at the bottom on a shell and "rested." He was leaning forward as he did this, but when he was swimming afterwards he was upright. We have an underground filter with penguin 550 powerheads that move 145 gallons of water per hour each (we have two). The current is so swift that it bangs them into the glass and turns them upside down. The one positive is that it doesn’t produce any air bubbles at all. However, I can’t imagine that a current of that strength could be good. How do we change this, and what should we use instead? Stretched out our horses are about 3 inches. I’m doubting the H. kelloggi simply because I haven’t been able to find any information on H. kelloggi and I have also been told that it is a species that is rarely bred and of which there is little known. I could be wrong – I am VERY new to this. They may in all actuality be H. kelloggi. Is there a chance that the color changing and strange movement could be courting? Also, there is a brown algae covering our tank, and spreading rapidly – is this just because of the horses? And is it dangerous for them? We have a few snails and some shrimp in the tank, but they seem unable to keep up with the problem, and I do NOT want to create a new danger for our horses. Thanks. Your information is priceless!