the problem with pH up products is that they are full of salts that come out when in contact with acids, so i would avoid them on soil, or any other medium where salts tend to build up.
a cheap option would be to get some sodium hydroxide from the hardware store, they sell it as crystals in tubs for unblocking drains, or sometimes as a concentrated (about 35-40%) solution. you will need to dilute this to about 5% so its easier to use and less likely to add too much to your res. a teaspoon of crystals in 100 ml of water would be about right, then add this a few mills at a time till your pH is ok. one tub will last years.