Actually, your pH is probably fien (some test kits measure low, like API) and Alk is already on the upper end of the scale (4meq/l=11.2dKH).
I have a large frogspawn colony with 11 heads right now. There would be 13, but when I added a new power head and timer, one head musta got irritated and it died. But the other heads loved it. When I removed the same power head a couple months later, a second head up and died. But all the other heads not only are doing fine, they continue to grow and divide.