A couple people asked me after my konjac sponge review if the sponges were alkaline, and wouldn't that be a problem if they were. Not having the bias of any marketing information (because I know very little about the sponges other than their functionality), my answer was based on my basic understanding of chemistry and biology: the pH of a dead plant remnant (aka a natural sponge) doesn't seem relevant, because you're soaking it in water, which has a pH in the neighborhood of neutral, depending on your city, and then combining that pH with the pH of your cleanser, and those two factors would be much more significant than any pH of the fibers.
I did a little research, and found out that the reason people are concerned about the sponge's pH is another example of sheer marketing bullshit. Companies selling sponges are advertising that the sponges are "100% alkaline", which is supposed to "balance the acidity of the skin", because apparently acidic skin is bad...? Of course, as I've explained previously, the skin's natural pH is between 4.5-5.5, and that's where it should be. The protective layer of oils I often refer to as the lipid layer is also called the acid mantle, and it needs that acidic pH to function. So the fact that these companies are trying to market what they're calling an alkaline product by saying it will fix your skin's acidity is just a reflection of their lack of knowledge, and should be ignored. And by ignored, I mean that you shouldn't give them your money.
But back to the sponge, what is its actual pH then? Well, the fact is that it doesn't really matter. It's just dead plant fibers. There's nothing about it that would give any meaningful alteration to the pH of water. Maybe the pH of the living plant was alkaline, but whatever the pH is of the dead sponge, it's completely moot. And in fact, it seems to possibly be a little bit acidic, if anything. Observe!