Sulfated or over-charged FLA gc2 batteries causing voltage sag.

[Dockers]

Does anyone know if extreme voltage sag under load is due to sulfation or loss of " active material ". Haven't found anything addressing this.
I have 8 duracell gc2 6 volt 230 ah in series (2 years, 10 m old). The typical ah draw is about 2-2.5 ah overnight. The " returned "ah is about 20% additional before the xw cc goes to absorb. A long absorb at about58.8v is needed to bring the sg to 1.280 or so. The finish current seldom falls below 2.6a @58v. (
When batts were new, finish current near .6a.) Absorb time:300 mins in summer. Winter max 480 mins.the batts are using about 1/2 gallon every 2-3 weeks. (Too much i believe- -- I'm in the high- desert area and the batts run about 80 f summer 50-60 winter. The batt case ends have bulged 3/16-1/4", the plates appear straight, however, what i can see.
The sg in 2 batts each have a cell thats stuck at about 1.200 sg even with multiple eqs. I dont want to needlessly over- charge the good batts. All seem to perform ok. The loaded V is about .100 less than the better ones. If i gently rock a battery the fluid is dark brown and rust colored. Is that normal?
Any comments are appreciated.

[Salts]

Dark brown and rust colored? Did you use distilled water or well water when you filled them?

[Dockers]

Always distilled. And that was when i rocked the battery
my reasoning: if eqing is to stir up and make the electolyte uniform, then this could be accomplished quickly without over charging .OF course not practicable in reality. Just wanted to see if would work. I got scared when all the particles were freed up--- didn't want to cause more damage. O