I had yellow shrimp for about a year before a tank disaster decimated them... But until then, they were happy and breeding (especially once I added Kent's Iodine to the water). Anyway, I had the same issue with the pH. I would be wary of the pH down product. Read on the label-- they say it's not good for plants. Because of this, I crushed Vitamin-C pills (ascorbic acid) and filtered water through the powder in coffee filters when I did water changes. It took a while, but I was able to figure out an approximate amount of Vit. C powder per gallon. I also had driftwood in my tank (which really did not change the pH significantly for me despite taking up about 50% of the aquarium space).
I have to admit, though, I was only dealing with a 5 gallon tank... But at least, I have proven that this method is safe and effective.