Don't alter your wax with high ph booster. Clean the tank out thoroughly and try again. If the wax is a newer polymer and not oil based it may benefit from strengthening the concentration product in the hydrominder tank. This is opposite than what you would expect,but the weaker solutions are attempting to bond with the water and can gel up.
Most people want their foam brush neutral ph , at least in the Summer months. Throwing copper scrap in the hydrominder tank will retard bacterial growth, but not eliminate it. Also try reducing your tank level if it's big. The goal is to increase turnover in the tank and not let solutions sit very long in there. If boosted with alkaline I would run it on the wetter side. Another thing to help is pick a rainy day, add some bleach to the FB tank and run it through the lines and let it sit and help kill the algae.
I know some operators that have added algaecides they got from pool supply places to their tanks.
Try to increase turnover of product in your HP soap tank by making the solution weaker yet drawing more product. If that and copper doesn't work, I would likely use any neutrals for foam brush and switch to a high ph high pressure soap. That reduces your problems down to one tank
If using 1/2" chem line the old turtle wax blocks would be an easy solution. I have some 1/4" plastic wyes and tees I can use on the smaller lines.