I haven't used AgaeCal, but used something similar, Pure synergy bone renewal based on red algae.

I had problems with over-active thyroid a while ago, I stopped taking the supplements but didn't know if they were implicated. Things settled down and I started taking the supplements again, similar symptoms, extreme tiredness, loss of weight, started after a year or so. I stopped taking, and returned to normal.

I mention this not to put you off, but for awareness. As far as I know algae derived calcium very good option. It may be very unusual to have my problem. I would be very interested to know if anyone else had a problem.

Despite all this I have managed to build some bone, and I hope I am continuing to do so. I am now taking d3, magnesium glycinate and K2. Also diet and exercise important.