Most of the information for the TDS of any Apisto breed would be listed with a description of the area and water they come from. If you are at 300ppm then You have to go way down. I would do it slowly for a 10 gallon tank about a 25% change with water adjusted to approx. 100ppm every couple days would work for me. Other people will have other opinions this is what works for me. When you tank reaches 100ppm and there is no response from fish then you work you way down from there until you reached the desired response. Make note of that and the pH if you would like it for your own future reference.
If you read about most Apistos their levels are 0 or less cacatuoides is one that is a little higher but not much. Usually if your working your way down to persuade your fish to spawn. You will know when you are at the right area for them. You see they didn't read the book so they sometimes don't go by it.