Where can I find some good large aquarium rocks that raise PH (outside) in the Los Angeles area?
In La, you usually only need to do water changes to keep up your pH. We have very hard water. If your pH is low, adding rocks to increase the alkalinity won't solve your problem, you have some other issue, or are not maintaining the tank/pond properly. You have too much waste or debris , and need to do some normal maintenance. coral rock, limestone, coral gravel, lace rock, all are sold and will raise the alkalinity/hardness of the tank which helps to buffer the water against shifting pH.
I've heard that LA tap water is pretty hard, and therefore, presumably, has high pH. But if you want more buffering in your water, you will want to use calcareous rocks (those that have a large component of calcium carbonate in their makeup). I don't live in California, so I don't know where to look for such rocks in the wild, but you can usually find them at places that sell stone for landscaping and construction purposes. Enough stone for an aquarium, or even a bunch of aquaria, is usually quite cheap at such places (at least, it's much cheaper than the same stone at an aquarium store). Coral skeletons and mollusc shells are made (mostly) of calcium carbonate, so they are possibilities. Some sedimentary rocks are made of fossil corals and seashells, so they should also be considered. Some rocks in this category that you are likely to find are: Limestone Dolomite Aragonite Tuffa Chalk Oolite Travertine (Technically, these are all kinds of limestone.) One favorite for aquarium decoration is Texas Holy Rock. It's limestone with a lot of natural holes in it. It probably occurs in places other than Texas, but the examples I've seen are from the Texas Hill Country (central to southern Texas). The holes provide more surface area for the stone to react with aquarium water, and also a lot of caves for fish (such as cichlids or catfish) of varying sizes to take shelter. I've seen similar rock called lace rock or honecomb limestone, and these are also good. There is a fairly easy test to see if a rock is calcareous. Get some sulfuric acid (from a scientific supply store) and drop a few drops on the rock surface. If the rock fizzes and bubbles, it contains calcium carbonate, which makes it a good rock if you want an aquarium with a high pH, and a bad rock if you want an aquarium with a low pH. Some people use full-strength vinegar or other acid substances for the same purpose. Vinegar often works, but a stronger acid will give you a faster and more obvious reaction.
