What ppm scale are you using? That must be 500 scale? Are you starting with RO? Maybe you need to up that calmag, been running 4ml thru late veg into w4f to account for starting water. I had some a swing early on where it seemed like they needed more.
I went along with this from CC's site:
Method 1 – Top-Off Reservoir: Using a top-off reservoir makes it easy to follow weekly feeding schedules. The top-off reservoir should have a similar nutrient concentration than what’s in your hydroponic system or the following weeks nutrient schedule. For best results pH and EC/ppm adjustments should be done through the top-off reservoir.
I've added in as they've been feeding super slow into the control res which dilutes pretty well enough. It does seem like after a adding more when the ppm's drop down low, that the ratios of what's left and what's in there and how it adds in is not perfect and it's more of a getby till a full strength flush. I mix a full system refill in the topoff which holds another 10 gallons leftover after a refill, drain the system, fill from topoff and then as the plants feed and drink it drinks in that weeks nute levels and drinks it pretty consistently. PPM's just continually drop as time passes. As long as the PH doesn't start to tank down I let it eat. When I add in calmag/A/B I don't think it all really goes in with the same ratios. Or why do we always do calmag into RO first thing and wait before adding A to let it bond in. If you add calmag to to a full nute mix after the fact, does it still mix in as bioavailable to the plants or does it get bound up to some other chemical which throws it off? Holds me back a bit from wanting to keep adding. I figure if it's always circulating, as long as the nutrients are in the water at all they'll be drinking em up as it goes down if it's at 700ppm or 450ppm since there is so much extra volume of water/nutes in the UC vs a static dwc bucket. I wish CC would write out more on that and ppm maintenance needs more clearly.
With the injectors and addin, does your controller script account for the injection of ferts and allow mix time before trying to make adjustments? I have to remember to turn my bluelab to monitor whenever I add so it doesn't get too excited before it's all fully mixed up.
I have the full strength nute mix in the top off, no airstone though, that does seem like it would lead to some gross since you are pumping outside air in volume thru it and whatever nastys are in the air ends up in there too. WIth just a small recirc with water shooting back down a little manifold it keeps it mixed and fresh but the topoff is pretty much all tight to air and contaminates. Also no warmth from the warm air pump air so it stays much cooler. Do you have a chiller? Could plumb in a wort chiller into the water return out of the chiller thru the top off if temps were really crazy in the room.
A lot of things to cover here
First, I read a bit since my last post and discover a post/website that the guy, after 10 years, whatever the NPK ratio he was using, he was getting the same results over and over. So I let myself thinking about it a bit... and will try few things down the road.
Second, when the plants are eating more N than K, the ph tends to rise, if K is the main uptake, ph will drop. It's a matter of ion and there's nothing you can do about it, except adjusting the ph.
Third, a lot of sources are saying that "you need to feed the plant the good nutrient at the right time".
That brings me to my previous grows, the ph was mainly rising until really late in flowering, like 1-2 weeks before harvesting so I thought, maybe I add too much coco cal in flowering because I tend to have deficiencies in coco/cal when my grows start. So I lowered my coco cal input and plants are still fine, flowers look gorgeous, AND? Ph is now dropping... So I guess more K is uptaken than N and in flowering, that's better right? But, even if I lowered my coco cal, every leaves are still in good health. Flowers grows each days so I don't think there's an imbalance in the NPK ratio.
As for injection, I use a script that inject my coco cal at 0 minute of each hour, followed 3 minutes later by A, 3 minutes later B, 3 minutes later Mid. So plenty of time to avoid chemical reaction, it drops by the drop, not a big flow and the amount is ridiculous so not any shock or whatsoever on first plants next to the epi center. My ppm is rock steady, I only have to adjust from time to time, more frequently at the end of veg until week 3-4 of flowering then it's mainly steady until the last week. When I inject, ppm rises the more the stock solution A, it goes from 350-360 to 400-410 ppm then back to 350-360 with way enough time before it injects the B and so on.
I have a chiller since my first run in rdwc, it's totally crazy to avoid using one.
So, as for the main concern of ppm usage less intense after 2-3 days of flush, that doesn't seem to halt/stop the grow process, they are thriving. I'll just flush a bit sooner. I just did a flush after 4 days and I keep my injection ratio at the same rate it was before the flush, I'll see how it reacts.
I'm getting pretty amazing results so I'm changing things really slowly.
As for the flush, I use SI/COCO/A/B/MID, the one I let mix for few minutes is the SI.
Coco cal is mainly calcium, same nutrient found in A so there's no big risk to mix them quickly one after the other. So yes, I let mix a little bit longer between A and B.
It's a good way to maintain topoff (water pump with a "waterfall". it avoid the ph to drop (caused by co2 from the air, injected in water). Maybe that's what is causing some nasty thing to grow in there.
" If you add calmag to to a full nute mix after the fact, does it still mix in as bioavailable to the plants or does it get bound up to some other chemical which throws it off?"
With what I saw, injecting a bit less coco cal and ph changing its course, I tend to believe it's available to the plants.
