Dwc topoff question

Heya
So I have one plant in a 10 gal res, use about 6 gallons. She's been drinking a gallon a day, I've been topping off with ro ph'd water.

My question is I haven't had to change the res for almost 3 weeks now. The ppm stays at a constant 700 and after 24hrs it goes to about 850 then I topoff and it goes back up to 700. Has anyone experienced this? Does this mean she's not eating at all? There's no yellow leaves or signs of nute burn.

I would say that your plant is a light feeder and that you may have found her sweet spot with the nutes if she healthy. Nothing wrong with that at all. Keep it at that level until it's time to step it up at the next phase. Also whenever the water level drops and your TDS/PPM rises it means it using more water than nutes and when the TDS/PPM drops with the water level it means it's using more nutes than water.

They always take more water than nutrients especially because it's only 1 plant -600/700 ppm is perfect for DWC IMO. I think you are expecting your plant to eat more than she does which is good. If there are no signs she needs more or less as you say just add water for awhile to avoid salt buildup and/or nute burn. Once I find the sweet spot you are in I tend to leave them alone & just keep adding water until the next phase and/or harvest. The nutrient mfgers suggest changing out res every 10 days but I typically go longer because I know I have benes living in my res fighting root rot bacterias; see: Heisenberg tea sticky for more info . After 3-4 weeks your res should be changed... At least switch out 80% of the res capacity leaving the beneficial microbes in your res to continue eating up the funk.

Where did op say they were using organics? I must have missed that part. There would be no benes if using synthetics. Now im a nube but is it not better to change res at least every couple of weeks? Could there not be a build up of some elements and a lack of others over a period of time?

Sure there could be that's why you should change out your res every so often. I'm just saying that setting a rigid and arbitrary period of time such as "every 10 days" is too finite and only serves to sell more nutrient to unwitting growers. The nutrients don't stop working after 10 days- but- there could be a buildup of bacteria and/or excess unused nutrient(salts). The plants don't care when you change your res- you can reduce the chance of root rot & increase your ph stability by adding beneficial microbes as recommended in the hiesenberg tea sticky.
3 weeks is the right amount of time to change out nutes if you were adding ph adjusted water since your last res change in a DWC IMO. Unless there is some other reason to change res like going to flower cycle or flushing in prep for harvest or whatever I don't see the need to do it EVERY 10 days. Of course you could go ahead & change out your res as often as you like ...just as you could choose to run nutes at the maximum ppms all the time if so desired. Typically I try to maintain 600-700 ppms in DWC even though 1100+ ppms are recommended by the manufacturer. If I went every ten days & used the ppms recommended I would be using up nutes by the gallon which is both unnecessary & wasteful plus increases the risk of burning the shit out of them.

change your water/nutes every 7 days, youll see increased growth rates compared to your addback method. promise.

heres a page i really liked reading https://www.rollitup.org/newbie-central/103677-ph-other-plant-problems-solutions.html

RL420 said:

change your water/nutes every 7 days, youll see increased growth rates compared to your addback method. promise.

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Hmm now you got me intrigued; ... I'm curious to see if it changing out nutes every 7 days noticeably increases the growth rate...when I re-up on nutes in the coming weeks & my current grow is harvested I'll give that a try

The idea behind this is that after so long, you'll throw the NPK ratios out of whack. Not so much an issue when the plants are young and barely feeding though..

Glaucoma said:

The idea behind this is that after so long, you'll throw the NPK ratios out of whack. Not so much an issue when the plants are young and barely feeding though..

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+1 for this.. Actually you can risk the chance of toxicity because you dont know what your plants eat of the NPK..