Since August... PH was a little low, but I think that was due to the lack of a sand bed bc when I put a remote deep sand bed into the 55g drum the Ph went back up from 7.4 to a more respectable 7.8
I also tried the foam-rock thing a few years ago on another build and I was naieve enough to think that it didn't need to be siliconed into the tank... it did!! It floated!!
My point though is that I left the foam-rock outside for two years in direct SoCal sun and the parts that were not coated did discolor and then degrade... as did the actual waterfall/fountain that I made my wife. Places that were coated well had no issues.
Now, looking at the new tank where it is in the water, I think that a good layer of Coraline will also help to keep the UV off of the foam. Plus I did a double layer of Epoxy and sand... as I said, I went overboard to make sure this one worked properly.