Foam on top of starter
I developed a starter following the tartine method about six months ago and I use it strictly for making pizzas every weekend at home in a wood burning oven. I keep it in the fridge, I feed it on Friday mornings, mix the dough Friday early afternoon, shape dough balls Friday night, leave in the fridge and make pizzas on Saturday night. With great results.
Recently, my dough has not risen as expected, usually it doubles in size in 6-7 hours. I use 20% starter by weight in my dough mix, so after feeding 100gr each of water and AP flour to the starter I use it for 1KG of 00 flour and 650gr of water.
Also recently, my dough balls have been flattening out instead of holding a ball form... so after asking on other pizza forums it seems my starter is too acicid? and is curring through the gluten.
After reading that this can be fixed by feeding, I feed it in 12 hours intervals for 2 days and did notice after the 3rd feeding a white foam had developed on top of the bubbly surface of the starter. I discarded and havent fed again.
Is this normal? Is my starter ok?