Help on flushing

I have a question about flushing. My plant has been lagging and not doing too much. I have it in a 1.5 gal pot and some of the roots are coming of the top of soil. I did my 1st flush and wanted to make sure I did it right. I started off with a 1/2 gal of distilled water, SLF 100 and bio root. After thev1 gal I checked run off and it was at 5200 PPM holy shit that is high I found my problem. About 3 gals later I got it down to 1400 iPPM s that good enough for now I do not want to over do it. Tomorrow transplanting into a 2.5 gal air pot.