Uggh....yes, anything dissolved in the water raises TDS, but fish care much more about being able to breathe than they care about conductivity. When organic waste is in the water it is broken down by bacteria. The bacteria that perform this breakdown require Oxygen.
THAT'S HOW THE NITROGEN CYCLE WORKS => NH3->NO2->NO3
For those who are chemically challenged, look closely at the last two products. The O in NO2 and NO3 is Oxygen. NO2 has two of them and NO3 has three of them. Where do you suppose the Oxygen comes from to generate NO2 and NO3?
The correct answer is that the Oxygen needed to produce NO2 and NO3 is stolen by the bacteria from the water column and from the sediment.
What do you suppose is the implication of bacteria stealing Oxygen from the water?
The correct answer is that the fish die of suffocation, or if they do not die outright, then it weakens their immune system so that the pathogens that are ALWAYS in the tank have a better chance of infiltration.
This is the biggest killer of ornamental fish...by a huge margin. People are worried about Nitrate and TDS, which the fish have ample biochemical strategies against which to defend themselves against, but fish have not yet figured out how to breathe without Oxygen.
Water changes remove the Oxygen-stealing organic debris and at the same time it provides a gulp of CO2 to the plant leaves - who then produce more Oxygen to the water column and to the sediment.
So stop worrying about how much ferts are left over from your dosing. These chemicals do not steal Oxygen and they have only a very minor effect on the fish. Worry about cleaning your tank and removing the real killer - dirt.
Cheers,