First off, I'm not sure deionizing reverse osmosis water is the same as distilled.
Your way there is no way to ascertain what PPM you have.
Here's what you need to do (this way you'll accurately know what PPM you made).
1. make a 1M solution of sodium carbonate
2. get one of the recommended reducers on this site
3. get a current limiter that can be accurately set to a particular current for the entire run so Faraday's law of electrolysis which given the PPM of ionic silver you want, the amount of water and the current you're running will provide you with the time, in minutes, to run the cell to get there.
4. a silver electrode (anode)
5. a cathode (stainless or copper is what we use - other metals may cause issues or even be toxic).
6. a beaker or jar that holds the amount of water you want (GLASS, NEVER metal).
7. some lid that will hold all the electrodes in correct orientation for the entire run.
8. a power source (20-30v is plenty)
9. a stir plate if you have it. If you're running lower current (3-5ma) at room temp you don't need it. Higher currents you need to agitate some so that the silver oxide particles being produced on the silver anode dissolve in the water fast enough that you don't start precipitating out the silver particles. If you're making higher PPM's (above 20) you need a heated stir plate to keep the water up around 120-140F so the reducer works quickly enough.
Put the cell together, use Faraday's law of electrolysis to compute the run time, add 1ml of 1M sodium carbonate (electrolyte) per liter of water and stir well, set the limiter to the current you want to run (power supply limiters are very non-accurate - don't try to use it - get a high accuracy limiter) set your cell voltage to 10V by adjusting the cathode depth in the water to keep the cell voltage up over 10V at your desired current. You want the power source to the limiter high enough that there's no way the cell voltage plus the headroom requirement of the limiter ever exceeds or even comes close to the power supply voltage or the limiter will drop out and you will have absolutely NO clue what you made.
If you're making higher PPM's, add the reducer up front because you need to keep the dissolved silver oxide below 20PPM or else you run the risk of precipitating out silver oxide particles. For a 20PPM run, you can add the reducer once the run is finished but you're going to have to heat the result to around 120F to get it to reduce quickly (minutes). It could take a LONG time at room temp. Run for however long the Faraday equation tells you to and shut the cell down. You now have an ionic solution of silver of the PPM you wanted.
TDS meters are useless for measuring the PPM of ionic or colloidal silver. About the only thing they're useful for is testing the purity of your distilled water (seriously) and no they cannot be calibrated to measure colloidal silver PPM.
If you only made 20PPM, heat the solution to over 120F, add the reducer, stir and in a half hour or less (if you heat to 140F its more like 5 minutes), the clear solution will turn a yellowish color (apple juice, beer, something like that). Cap the jar, let it cool and you're done.
Now you have to decide whether or not you want to gel cap. For ingesting non-gel-capped colloidal silver, you lose about 25% of it do to the action of the stomach (it causes some of the particles to agglomerate into larger particles that cannot be absorbed into the blood). If you gel cap (procedure explained on this site - its simple), just about 100% makes it into the upper part of the small intestine which is where the gelatine is digested and the silver particles absorbed into the blood. Oh, and gelatine is a protein so animal based. Vegetable gelatine is NOT and won't work. IT will get dissolved in the stomach and you'll lose about 25% of the useful silver.
If you're making a liter of 20PPM, I'd suggest 10ma and run the cell for half an hour.
This is just a quick overview of the process we use. Its been scientifically tested to work properly every single time.