In ground vinyl lined pool chemical imbalance and black algae

I have a rectangular 16000 gallon in ground vinyl lined pool. We started getting calcium build up on the walls and then black algae where the shallow end transitions to the deep end only on the floor and it has attached to the what looks like calcium deposits which blanket the pool. We just had the liner installed 3 yrs ago. We brush regularly. We always treated pool with liquid chlorine - which contains sodium hydochloride of 10%. We have tried various shocks and algaecides and can not totally remove the black algae and are having no impact on the white calcium deposits. We had the water tested and the alkalinity runs between 250 and 280 with the PH at 8.0. The calcium level oddly is ok but the chlorine barely registers no matter how much we add. We were told to bring down the alkalinity and so have been using 2lbs of dry acid pre mixed with 1 gallon of water and scattered through out the pool and then having the pool pump run for 4 hrs(per instructions on dry acid). We did this one time a day for several days and only got down to 240 on the alkalinity but ended up at 7.8 or so PH. However the algae was not getting better nor was the calcium powder on the walls and floor even though we shocked the pool and continued to use the liquid chlorine imbetween and tried algaecide a few more times. We have taken a couple of days off from the dry acid and now the black algae is worse, the alkalinity is still at 260 and the PH has gone up to 8.0. The water itself is very clear not cloudy. I have just had all the equipment checked. We have cleaned the filter 2x's through the process. What do we do now without completely ruining our liner or having to re-line again after only 3 years?