Grow Mediums End of Life Nutrient Requirement

[Raggedy Man]

I have 6 autos that have a couple/3 weeks till they finish and am wondering about their tds requirement. These last several weeks the ppm remains stable no matter the strength. I was at a high of 500ppm at the peak and was adding quite a bit of nutes daily to keep it there, when the uptake began slowing I obviously didn't add nutes like I was before. Now, every morning the tds numbers are the same as the day before (ph is dropping steady as usual for late flowering). I would add fresh water and whatever strength the solution was left at that morning it would be the same the next day, no matter what I leave it at. I'm down to 380ppm now and this morning like every other morning lately it's the same as I left it the day before....380 in today's case. It's never higher or lower, always the same. I always have to add a couple gallons of fresh water to the rez and it drops by maybe 20 points. The next day it's holding steady again at that new number. Obviously they're taking in some nutrients because the ppm will have dropped slightly when I top off with fresh water. Do I keep on dropping the tds to find the sweet spot again or do I pump the "ripen" formula (per GH feeding schedule) to them?
Maybe I'm confusing the Lucas method to keep the tds at peak numbers (which I used several grows ago)? With lucas I obviously used grow and bloom only. This grow I've been using the complete lineup of GH nutrients and their feeding chart (at reduced strengths of course).

 

[Mañ'O'Green]

Hey there @Raggedy Man I have always just added enough nutrients back to the reservoir to match whatever I started the week with. So if they took in 10% I just add 10% back. I hope you have an EC meter and not just TDS they work similar but a TDS is for measuring solids in drinking water and an EC meter measures nutrients. I know potato pototo! but in hydro there is little room for error.

It is really cool that when the plants kick in to full flower they drop the PH in the soil/res to signal the microbes to make more P-K. This is the time to switch to your bloom nutrient formula.

Pictures?

 

[Raggedy Man]

Hey there @Raggedy Man I have always just added enough nutrients back to the reservoir to match whatever I started the week with. So if they took in 10% I just add 10% back. I hope you have an EC meter and not just TDS they work similar but a TDS is for measuring solids in drinking water and an EC meter measures nutrients. I know potato pototo! but in hydro there is little room for error.

It is really cool that when the plants kick in to full flower they drop the PH in the soil/res to signal the microbes to make more P-K. This is the time to switch to your bloom nutrient formula.

Pictures?

So THAT'S why the ph drops during flowering. If they only knew I can give them as much P-K as they wanted I wouldn't have to fight with it every 3 months.......
I suppose I could switch my monitor (pictured below) to ec but I use it only to determine if they're over or under fed (duh, I guess everyone does) so any number or scale works for me. If the numbers drop overnight I increase nutes, numbers climb, I decrease. Every grow it seems the ppm max changes as I plant at least one different strain each time, looking for the "holy grail" of insomnia meds. I suppose if I was better educated in the whole ec, tds, ppm thing it would all make better sense but right now at 380 (500 scale), 510 (700 scale) or .7 ec are just numbers that I refer to each day to see if I need to add nutes or clean water.
The open spot in the one picture is where one was an overachiever and was ready earlier than expected. Today is the beginning of week 12. Also had one giant cola top I found rot in and cut it off. I did check the others and they were ok for now

 

[Mañ'O'Green]

not only is that an EC meter it is as good as it gets. They are just calling the Hanna scale the TDS scale. Lots of cheap TDS meters report in Hanna. This is an equivalency chart.

There are other factors that cause the PH in the reservoir to change over time. One of them is the aeration of the water causes some of the calcium carbonate to precipitate out this will cause the PH to go down. Nutrient's organic activities can cause it to go up? We almost have a primordial soup by the end of seven days when we change it out.

I use a Blue Lab combo meter as my main tool. I have a PH pen and Back-up probe for the meter just in case.