So far it seems that all the responses are correct. I also see you have a "more then sufficent air stone'. Aire stones are not generally used in SW
tanks. You want to add a power head or two to circulate the water and create a rippled surface. The airstone adds oxygen to the water only when the bubbles break the surface. But it also causes additional salt creep.
Get a refractometer to test your salinity. Swing arms are generally not consistent. As stated you want an SG
of 1.022 - 1.026 and that shoud be stable, not fluctuating.
The star losing limbs was probably due to osmotic shock from SG
changing too quickly, or beyond it's livable range. Once they start doing that they rarely recover.