So 2 times in an 8 wk flower period might be good.
But did you use a product like forakleen against the salt built up when you didn't change the res? Actually please tell me how did you notice salt built up?
Actually I googled a bit more and did find another variant:
There are two ways to work with this formula:
1. Top off the reservoir daily using a pH corrected water solution as required to maintain full reservoir level. After adding back an amount of water equal to the amount of your reservoir capacity you should change the reservoir and put in fresh solution.
2. Top off the reservoir daily using a pH corrected 100% strength nutrient solution as required to maintain full reservoir level. Continue to use this nutrient solution without dumping the tank unless the PPM rises above acceptable levels.
https://www.rollitup.org/t/general-questions-on-the-lucas-formula.272729/
compared to the (wishful thinking
) method which I mentioned before:
Advanced Add-Back method:
If you have a EC/tds/ppm meter you can increase your yield by maintaining a constant level of nutrients throughout the grow. This is done by periodically adding back nutrients to your reservoir and works best when used in combination with a float valve to continually keep the reservoir topped off with RO.
Additional Note: DO NOT check pH or TDS/PPM/EC without first making sure the res is topped off.
Those numbers are useless to you and will only confuse you until you fully understand. (They’re still useless to me. LOL)
https://www.icmag.com/ic/showthread.php?t=124487
The difference between these to seems to be that they first method tops off with water that is ph corrected and has already 100% strength nutrients in it. Which would mean that after some time the PPM in the res will rise. I guess that is because the plants consume more water than fertilizer?
In the second version it is claimed to never change the rez when correcting ph and nutrients after topping off. You try to hold the ppm at a certain level.
@HydroRed Can you please tell me how you add your nutrients? After topping off or before? And are you using Reverse Osmosis water?