My well water is at 7.5, I've got 2 inches of water above the silt. I do have npk tabs I picked up with the ph test. Early on. Just have to dig them out, I've got access to wood ash.
do the NPK test first,my well water is pretty high too, PH 7.2 PPM 315 i have NPK all at adequate,PH 6.5,for soil mix, i get a balance from the 6.5 PH of soil,thats why i work hard to keep it there,when it does rain here,water go as high as 8 from the aquifer,then i have a few issues,so to adjust the container garden ,i collect condensor water from house ac and half well and half condensed water for adjustment,i guess what im getting at is if your soil ph and NPK values are right the soil will buffer that 8 you have but want like it,it too late now,but i mix peatmoss in the soil to drop ph,if i have a drastic climb a tbsp od sulfur to a 18 gal container and it drops the ph slowly,there is acidfier,same as sulfur imo,but you have a lot of math to do with it and im no chemist hgahahah so 1 tbsp sulfur water in wait it out 2 weeks check again,if it didnt move at all you have a drainage problem,the sulfur will green the plant up,but it also should move ph a point at the least,all this mentioned is what i think you got ,looks like cal mag yes,bugs hell ya,all the stuff going on is from soil ph and intake of water,you probally got a lot of calcium and magnese,its locked up from the high ph