Fish can tolerate a much wider range of water conditions that you might think, provided you let them acclimate to it. Using products like pHup is going to make it very hard to keep the pH stable, and fluctuating water conditions like that will in the end be more stressful on the fish than a pH a little out of their range. If your pH is 6, it's not so bad as you would think. Your silver dollars are comfortable in the 5.0-7.0 range, so they will have no problems. Similarly, the pictus cat like 5.8-6.8 (7.0 is actually a little alkaline for it), the rainbow shark like 6.5-7.5 (6.0 isn't far enough out to really stress it) and mollies, though they like a pH of 7.0-8.5, are notoriously hardy little fish, and will likely adjust just fine over time. The only real side effect of an innapropriate pH will be that the fish are less likely to breed and reproduce, but unless you are wanting this, it shouldn't be too big of a deal. One thing to keep in mind is that the average range for stream water pH is about 5.5 to 7.5, and a lot of freshwater tropical fish will have lived in streams in the wild.
If you are still concerned over your fish and the pH, you do have better options for raising the pH in your tank that doesn't resort to chemicals. Make sure your water is well-aerated (get a bubble wall or an airstone if neessary). To much CO2 in your tank will lower your pH and your fish will love all the oxygen in the water. Also keep up with cleaning a little more thanyou otherwise might, since decomposing matter in the tank will release carbonic acid into the water, which acidifies it. You can also add coral or limestone to your tank, either as decorations, or in the filter, though the former will likely be a lot simpler. Some people even use a coral-based substrate. I believe this leeches calcium into the water, which raises the pH.
Something to also read up on is buffering your water. The more buffered your water is, the less drastic any pH fluctuations will be. See what looking around the internet for water chemistry and kH and gH will get you. I personally don't have a lot of knowledge in this area, so I can't really help you out there.
Good luck with your fish!