Aquasolum is a buffering substrate, which explains why your pH is so low...
It's recommended to use remineralized RO with buffering substrates. Using the proper remineralized RO, buffering substrates may last 1-3 years, if not longer. Using tap water, buffering substrates may last less than a year.
Planted tanks and shrimp don't always go well together, since they enjoy oxygen enriched environments. If you don't plan on going the CO2 route, you'll probably be fine.
That said, the cherry and rili shrimp you have do best in higher pH water. They can, and do, live and thrive in water at that pH, but if your shrimp aren't reproducing, you may want to consider a shrimp only tank for them.
Not only that, but cherry and rili shrimp are two different colors of one species. If they breed together, there's a chance of "wild colored" offspring, and if you don't cull them (i.e. set up a cull tank or give/sell the shrimp away), it's possible for the colony to turn wild type over time. If they don't ever produce wild type offspring, you'll be fine!