[HighlandReefer]

rtecanoe,

Glad you shared your experience with the AlgaeFix Marine. I assume you are using the Marine product?

The manufacturer states that AlgaeFix Marine will slow down the growth of chaeto and macroalgae, but should not kill it. Why your chaeto is being affected may be do to the AlgaeFix or perhaps other factors are coming into play. Chaeto will suffer (but should not die) from lack of iron and if your nitrate/phosphates are extremely low, IME. You are the first hobbyist that I am aware of that has had chaeto die while dosing AlgaeFix Marine.

Nitrates and phosphates are taken in by algae as it multiplies. If the algae dies and the dead parts are not removed, then the dead parts will brake down into nitrate and phosphate, simply stated. If your nitrate and phosphate increases, then I would recommend taken appropriate actions to lower them.