Just switched to Lucas formula 0-8-16 in rockwool after many sucessful runs with H&G in a UC. I know the target ppm in RO water is 1300ppm but i'm not sure what setting to have my meter on. It is a HM COM-100 and has the following settings:
Switching EC Modes: The COM-100 has three different modes for EC: KCl, 442TM, and NaCl. Note that this setting only changes the ATC coefficient that is used. To change the EC mode: 1. Turn the meter on by pressing the ‘ON/OFF’ button. 2. Press and hold the ‘HOLD/MODE’ button. The meter will cycle through the following modes: a. EC – KCl b. EC – 442TM c. EC – NaCl d. TDS – KCl e. TDS - 442TM f. TDS - NaCl 3. When the meter displays the desired selection. Release the ‘HOLD/MODE’ button. 4. The meter is now ready for use in your selected mode. The meter will keep this setting until changed again. Switching TDS Modes: The COM-100 comes with three TDS modes, each with its own EC to TDS conversion factor and Automatic Temperature Compensation coefficient. To change the TDS mode: 1. Turn the meter on by pressing the ‘ON/OFF’ button. 2. Press and hold the ‘HOLD/MODE’ button. The meter will cycle through the following modes: a. EC – KCl b. EC – 442TM c. EC – NaCl d. TDS – KCl e. TDS - 442TM f. TDS - NaCl
I would NEVER run that hot in rockwool. To answer your question.. just use EC. I mean the TDS reading is just the meter converting the EC number to something else.
I have run exactly what you're doing.. rockwool with regular lucas. For me, I would never go higher than 1.3 EC or so. (Which is around 850-900 PPM)