Lowering PH, a safe method?

Lowering pH is possible by three major methods:

1) Peat moss. The effect from this is real, but it requires frequent changing and rather large quantities of peat moss compared to other methods. Like you said, it adds tannins, but many people find the subtle coloration to be desirable.

2) RO filtration. Since pH is really a function of buffering capacity, lowering it requires a reduction in the carbonate hardness of the water. The most practical way to do this is to use an RO unit to remove dissolved salts (including carbonate). When the KH drops, pH follows. Distilled water can be used too, but it's a bit impractical for anything larger than a nano tank.

3) Addition of a strong acid (HCl, H2SO4, HNO3) will effectively "consume" buffering capacity, lowering KH and therefore pH. This method is perfectly effective, but in actual practice dealing with strong acids is dangerous and prone to rather grave errors over the long run.

CO2 addition will also drop pH, but the effect is "artificial" in a sense. Provided you keep the CO2 levels in a safe range, as far as fish and inverts are concerned, it's really the buffering capacity (KH) that affects them biologically.

I use collected rainwater to lower the ph in my tanks, and tend to add hardwood and (previously boiled) peat (generally under the substrate) in my softwater/low ph tanks.

I also used to notice ph dips when I was fry-feeding with vinegar eels, so small ammounts of vinegar(drops at a time) shouldn't harm your fish...but beware of manually adjusting ph. Depending on the buffering capacity of your water...adding equal ammount of an acid 4 days in a row can do nothing for three days, and then radically swing things on the fourth. (due to finally overcomming those buffers). It can also turn into a constant battle...if the water you're adding to the tank is constantly raising the pH, you'll get into a seesaw effect of constantly raising and lowering things that is probably worse of the tank than your current pH level?

In a planted tank, I'd probably just add a DIY CO2 reactor...it'll lower your pH and also help out the plant growth.

On a side note, I've kept quite a few different kinds of freshwater shrimp, and wouldn't personally consider 7.6 something that needed adjusting? (in fact, I have Cherry Reds that breed fine at over 8...your milage may vary...)

Best of luck!

Cliff