The blue tube thing is your R.O. membrane, which is different than the D.I. cartridge. The R.O. membrane on your filter should be horizontal, sitting above the 2 vertical canisters which should hold a prefilter and a carbon block. The flow from your faucet should go into the prefilter, then into the carbon, then the R.O. membrane. Coming out of the R.O. membrane is a waste hose and an output hose. The output hose should have 10% or less of the TDS that your source water has; 25ppm TDS is about right for tap water in San Antonio.

Then to get to zero TDS, you go from the output of your R.O. membrane into the D.I. cartridge. The 1st 2 products you listed are the best way to refill your D.I. cartridge.

Expect to get a couple hundred gallons from a D.I. cartridge; any more and it will be exhausted. If your R.O. was not functioning, meaning if you were sending 200 ppm TDS to the D.I., it would still get the water close to zero but would get used up MUCH faster. The other thing to watch out for is make sure that your carbon block is in good shape, as it removes chlorine which will damage the R.O. membrane.

You might give Bryan at purelyh20 a call. He's very knowledgable and helpful on the phone. It would not be a bad idea to just get all new filters from him; 1 micron prefilter ($5 I think) a new carbon block (not much) and the D.I. stuff. Probably your R.O. membrane is okay, but what you should do is disconnect the line from your R.O. output to the input of the D.I. and test it there. Make sure it's 25 or so at that point. If it's much higher, get a new R.O. membrane too. It's worth testing because that's the expensive one.