Blueberry: Weak growth and reddish leaves
New growth on my blueberry plants look somewhat weak and have light green and reddish leaves. The leaves on the old branches are nice and green, but it seems to take a lot of time for the new leaves to get dark green. The ph is somewhere between 5.5 and 6.5. I've been water them with sulphuric acid (ph around 5) every other day to lower the ph, a cup or two.
I have one blueberry plant that is planted in a soil made up of peat moss, pine mulch and perlite. pH is somewhat lower, but the plant is growing just fine. Very few red spots.
"MasterGardeners" recommendation (https://www.youtube.com/watch?v=1BHX-Tvfdrk)
Exactly what is the problem? What does it need?