fiber glass is defo the best option, it may cost more but the finish on it is 1000% better and you will not have to worrie about any leaks that you may get with a liner.
/Neil
Sorry for not replying sooner. This basic test shows if there is any calcium present in the rock, if it bubbles this is a chemical reaction that shows it is present. As such, any rocks that react should not be used in an aquarium as the calcium will leech into the water and affect ph or...