Most of the commonly available pH modifying products contain phosphates, your algae will love you for them. Things like bog wood etc., can drop your pH if your water is not terribly hard or buffered, where I live, it would do nothing other then look good.
If you want to modify your pH, you REALLY need to understand how pH, hardness, CO2 concentration, buffering etc. are interelated. You can create perfect pH water that is so unstable, it will swing by as much as a couple of degrees in a few hours, if your buffering is incorrect for example.
Also remember that fish bought in the lfs are almost certainly in tap water. Putting them into a tank with drastically different water conditions will be stressful and can cause death by osmotic shock among other factors. Fish need to be aclimated slowly to the new conditions. How long depends on the fish and the deltas.
As far as I am concerned, the only long term solution to producing water of defined characteristcs is to buy an RO unit. You can buy RO water from some lfs, but it is a very uneconomic option. People on metered water supplies should work out in advance how they are going to use the waste water from the RO, as the waste water is substantially greater buy volume then the pure water produced.
