Hello,
This is yet one more myth that hobbyist should never worry about. pH is just a number and has no meaning by itself and is only relevant within the context of the chemical agents in the water. So the number itself cannot be dangerous unless the number is being driven by a dangerous agent in the water column. This is a concept that many people completely misunderstand. So for example, suppose you were to put battery acid in the water. It would drive the pH very low and would be lethal to the fish, but the fish would not perish as a result of the low pH. They would perish because of the toxic acid. Similarly, suppose you put ammonia in the water. The pH would rise, but the animals would perish due to ammonia toxicity, not due to pH rise.
This is a really important concept because it forces us to look at the reason for the pH reading and to not necessarily be alarmed at the numerical value itself. Since we are not introducing any toxic agents into the tank that coincidentally also have an effect on pH, then there is nothing to worry about. Just like the behavior of your TDS reading, it is not the number itself that is necessarily an issue, for example if it were due to calcium in the water, but if a large portion of the number were due to pollution, i.e. fish waste and uneaten food, then yes it would be a worry because pollution kills, not TDS numerical value.
Cheers,