Question about replacing water in DWC

[Grand Daddy Black]

When your plant starts drinking so much that you need to replace water between feedings, what's the best approach? Do you top off the plant with plain ph'd water or water with a reduced nutrient solution?

 

[Barney86]

Niether mate.
The idea with feeding in hydro is you want to keep the ppm number steady as they feed.
If ppm rises then the plant is absorbing more nutes than water so the mix is getting stronger.
If the ppm drops more than a little then it's absorbing more nutes than water so the mix is getting weeker.
You want to mix the feed to the right strength so that the ppm iether stays the same or drops just slightly from day to day.
Then top up with the same strength feed.
That's how to keep the Res as balanced as possible. It also keeps the pH as stable as possible and you have to do Res changes less often.
The magic number, assuming the plants are growing properly is around 100ppm per week of veg.
Post a full plant pic so I can see the size and I'll be able to give you a pretty accurate guess.

 

[Grand Daddy Black]

Niether mate.
The idea with feeding in hydro is you want to keep the ppm number steady as they feed.
If ppm rises then the plant is absorbing more nutes than water so the mix is getting stronger.
If the ppm drops more than a little then it's absorbing more nutes than water so the mix is getting weeker.
You want to mix the feed to the right strength so that the ppm iether stays the same or drops just slightly from day to day.
Then top up with the same strength feed.
That's how to keep the Res as balanced as possible. It also keeps the pH as stable as possible and you have to do Res changes less often.
The magic number, assuming the plants are growing properly is around 100ppm per week of veg.
Post a full plant pic so I can see the size and I'll be able to give you a pretty accurate guess.

Thanks for the feedback, @Barney86. I don't think I have the kind of set up you're talking about, with a separate reservoir. I am running individual buckets and changing the water weekly with fresh nutes. When the plants are in the late stages, they start drinking almost all the water before it's time to do the weekly thing. So my question is about the best way to replace that water until it's time to re-feed.

 

[Barney86]

Thanks for the feedback, @Barney86. I don't think I have the kind of set up you're talking about, with a separate reservoir. I am running individual buckets and changing the water weekly with fresh nutes. When the plants are in the late stages, they start drinking almost all the water before it's time to do the weekly thing. So my question is about the best way to replace that water until it's time to re-feed.

Nah I'm talking about your set up mate.
I don't 't use a Res iether, individual NFT systems. All hydro systems follow the same rules though, including coco.
You just gotta follow the ppm number. Keep it steady and top it up with exactly the same as you started with.
You'd treat a top up Res the same way though. People say you need to top up with half strength and whatever else but it's only because they don't know you're supposed to follow the ppm.
It's your golden tool mate. Tells you everything you need to know.
If it goes up you add more water.
If it goes down you add more nutes.
The ppm should be the same as it started when the Res is almost empty.
Doing it this way gives you the best growth rates, healthiest plants and least chances of Def or toxicity issues, means you shouldn't have to adjust the pH between feeds too.

 

[Grand Daddy Black]

Nah I'm talking about your set up mate.
I don't 't use a Res iether, individual NFT systems. All hydro systems follow the same rules though, including coco.
You just gotta follow the ppm number. Keep it steady and top it up with exactly the same as you started with.
You'd treat a top up Res the same way though. People say you need to top up with half strength and whatever else but it's only because they don't know you're supposed to follow the ppm.
It's your golden tool mate. Tells you everything you need to know.
If it goes up you add more water.
If it goes down you add more nutes.
The ppm should be the same as it started when the Res is almost empty.
Doing it this way gives you the best growth rates, healthiest plants and least chances of Def or toxicity issues, means you shouldn't have to adjust the pH between feeds too.

Please be patient with me @Barney86. I'm trying to understand what you're saying.

Let's say I need to top off a bucket. The ppm number has dropped to half of what it was. Do I top off with the same nutrient level I started with or half of the nutrient level I started with? Or maybe even double the nutrient level I started with?
I'm new at this! (Just in case you couldn't tell.)

 

[Gadfly]

When needing to top off, just add some of your base fert in small doses to bump it back up to the correct ppm and then adjust ph. Steady PH was a critical for hydro. If your PH is out of wack, ppms are meaningless because the plant cant utilize anything. Don’t double up your nutes in the beginning unless you want to risk frying up your plants. Hopes this helps.

 

[Barney86]

Sorry mate, I sound a bit abrasive sometimes. Just the way i comes across. Don't mean it lol.
It takes a bit of trial and error, you'll get an "ahah moment" after working it out a few times.
Yeah, so if the ppm dropped by half then top up with about 50% more. If it dropped by a quarter then make it about a quarter stronger.
Make a wee note of what the change was and on Res change day try and adjust the feed to avoid the change.
If you post a pick up I'll be able to tell you pretty accurately how strong it should be and just take it from there. Save you a couple weeks of figuring it out.

 

[Dro]

@Grand Daddy Black I struggled with the same question and concept for some time as you. The idea is to keep ppm level the same through out the week so this what I do and learned this from @Rifleman

These are my numbers for this week:

Starting ppm and pH with reservoir full:
4/6 1240ppm @ 5.5pH

From here I monitor water level through out the week and check ppm and pH.

The numbers that I will show below are taken with full reservoir after adding water everytime. What I didn't write down (and I should have) is the ppm reading before adding water as this will tell you which way to go about it. I also keep a running count of the amount of water they use and that is why you will see a +amount =running total

4/8 +2qts. 1220ppm @6.2pH. Lowered pH to 5.7
4/9 +2=4qts 1210ppm @5.7
4/10 +2=6qts 1220ppm @5.7
4/11 +2=8qts 1050ppm @5.5

So as you can see, Everytime I added the +2qts my ppm stayed around the same. This happened because my ppm before adding the 2qts was higher than 1220ppm (1350ppm if I remember correctly)

Now you may be wondering what happened to my last reading. Ppm after adding +2qts was lower than the target 1220ppm. This tells me that the plant has eaten more than what she drank. My ppm prior to adding +2qts of water was the target 1220ppm so obviously adding it diluted my nutrients and the end number was 1050ppm.

So here is where some people go different routes and you will get different opinions. I could have tried to match the ppm by adding pH water plus some nutes but how do I know what nutrient out of the whole mix the plant drank? I don't so I am not going to try to guess. I err on the side of caution here so instead I just add plain pH water. Why? Because of a couple of reasons. 1) my res change will be Saturday and she will get a full res change. No need to panic here. 2) the plant is drinking and using up the nutrients needed, to add more nutes at this point is like giving a kid a plate full of food after she has finished her peas only...

The key here is making sure you change your res weekly to avoid nutrient deficiency (which could happen with the approach above) or nute lock out (which could happen by topping off with nute water). Unless you have lots of experience and can tell what nutes the plant is needing through out the week I would suggest sticking with just pH water.

I hope this helped you out, I know it was a bit long winded but I struggled with this and finally it clicked after reading @riflemans journal (start in post #2559). Go check it out if you have a chance, lots of good knowledge over there!

 

[Dro]

Fyi, this is a good guide that helps you determine what is happing based on your numbers

 

[Rifleman]

Thanks for the plug @Dro. I'm pretty sure I posted the notes for the chart in my journal also.

 

[MidnightMann]

Good information but think geared toward those with separate Rez. If you are doing weekly bucket changes then yes late in flower you will need to add water, I would just add water then PH to 5.8. that will get you fine through rest of week until full water change

 

[Grand Daddy Black]

Sorry mate, I sound a bit abrasive sometimes. Just the way i comes across. Don't mean it lol.
It takes a bit of trial and error, you'll get an "ahah moment" after working it out a few times.
Yeah, so if the ppm dropped by half then top up with about 50% more. If it dropped by a quarter then make it about a quarter stronger.
Make a wee note of what the change was and on Res change day try and adjust the feed to avoid the change.
If you post a pick up I'll be able to tell you pretty accurately how strong it should be and just take it from there. Save you a couple weeks of figuring it out.

You don't sound abrasive, @Barney86! I just feel like I have too many questions and might be a little slow on the uptake. I've done a lot of reading about PPM and PH. I understand the PH concept but don't quite get the PPM strategy. My plants are just babies now (14 days old), so it's not really an issue yet. I'm just trying to figure out the proper thing to do later, when they really start drinking a lot. Here they are:

 

[Barney86]

Ah hell yeah mate they're nice n healthy. I was expecting there to be some sort of dramas lol.

I know it's a lot to take in at first, I was in your shoes a few years ago. Was completely stumped and my first hydro grow was already falling apart by this point. Spent a while on another forum being baffled by techno jargon, then a kindly Scotsman decided to pull out the sock puppets for me and explain it without all the science bullshit and turned my stunted, half drowned, N toxed auto into a beast.
You've got no dramas to start with so I'll aim a little higher

Right so, ppm is parts per million. It's a measurement of the total dissolved solids (TDS) in a liquid. Basically tells you how much nutes are in the water.
Now I've no idea why, but depending on where you are in the world this can have 2 different values. I'll explain shortly.

You'll also see people talking about "E/C" when referring to nutrient strength.
E/C is basically the same thing as ppm but only measured on a 1/10 scale.
So you get 0.1-3.0 e/c instead of the much more accurate 1-1000ppm.

The meter works by testing the electrical conductivity of the water, E/C.
As I mentioned, different places have different ppm values and here is what I meant.

I'm in the UK (Scotland) and we, most of Europe and some places in America buy meters that convert 1e/c into 500ppm.
Other places in America, Australia, and some random foreign countries convert 1 E/C into 700ppm.

That's a pretty big difference so if you have an e/c setting on your meter could you tell me what that says you're feeding them and also give me the ppm number.
Plants that size should only need around 0.6 e/c, ppm is a better way to measure it but the answer depends on where you live lol. How wierd is that.
Oh also, i need to know the reading on the water your giving them before you put anything in it.
That can have a pretty massive difference on your reading so need to subtract that aswell.

Sounds complicated at first mate but honestly, give it 3 or weeks and you'll be doing it without thinking.

How old are they by the way? 3 weeks roughly?

 

[Barney86]

Haha quality just realised you said they're only 14 days. Can't really get much of a better growth rate than that. Well done sir.

 

[Barney86]

Fyi, this is a good guide that helps you determine what is happing based on your numbers

Boom!
Best way I've ever seen it written down.
Only saw it for the first time last week. Get the admin to sticky that in the hydro section somewhere, would save a lot of explanations lol.
He should go get a job with a nute company and show them how to write an effin schedule
(Edit) just read it again and he seems to have missed the differences with veg and bloom.
If the ppm level is fairly close to perfect. The pH should rise during veg and drop during bloom while the Res level drops.
Makes a fair difference to a couple of those points.
Still really good guide though. It's almost perfect.

 

[Canuckush]

Mark for reference later! Great info growers!