Acans in trouble

[GlassCityReefer]

I have 2 acans that I am worried about but 1 is really bad, I don’t know if it is possible to save. The tank got overrun with algae and cyano. I took my time trying to take care of it with water changes and vibrant. They just started receding more and more and I was worried about losing them all together so I started running gfo and put in chemi-clean. The algae is almost gone and the cyano is gone, parameters are good and I am doing water changes weekly of 25%. The tank is a 20 gallon Nuvo. I really wanted to keep from having to run gfo but was worried I would lose everything. Any advice would be appreciated. Parameters are
Salinity 1.025
Dkh 9.3
Alk 8.2
PO4 .07
No3 4
Calcium 480
Ph 8.2
Any help would be appreciated... have had them for almost 3 years.
Light has just been turned on when I took the photo on top.
Here are the before and after pictures.

 

[Hemmdog]

What is your magnesium? What do you feed them and how often? What light do you run?

 

[GlassCityReefer]

I usually don’t feed them on top of the mysis shrimp they get that fall on them from feeding the fish. Magnesium is a little low at 1200 and I run. The AI prime

 

[Hemmdog]

I usually don’t feed them on top of the mysis shrimp they get that fall on them from feeding the fish. Magnesium is a little low at 1200 and I run. The AI prime

Get your mag up.