[Randy Holmes-Farley]

Yes, organisms may concentrate potassium to some extent , but they do not deposit it like calcium, magnesium,or carbonate. Nor do they make organic materials out of it, like nitrogen and phosphorus. It is just incorporated as part of the salts that exist inside of cells.

The thing that bothers me about the whole idea of depletion is that feeding foods that are made from plants and animals ought to add back potassium in similar ratios to that which is consumed. The nutrients (phosphorus and nitrogen) that fuel algae growth ought to be coming in in ratios to potassium that are roughly similar to what is used up in growing new algae. So perhaps the balance is imperfect for some reason, but it is far from as simple as saying that organisms take up potassium so it should get depleted.