PH is dropping about halfway into the week — after the weekly reservoir and nutrients change

Context:
Currently in week 9 after germination, at about day 60. Plant is the ILGM Blue Dream Autoflower. Well into flowering stage. Plant is in a 5 gallon DWC bucket that is topped off with 3 gallons of RO water daily. Right now we are adding about 1 - 1.25 gallons of RO water a day to top off

Problem:
PH is dropping about halfway into the week — after the weekly reservoir and nutrients change

What I tried to do:
I thought that salts might be building up in the water so once the PH starts dropping (about 3 - 4 days since last reservoir and nutrients change) I do a full water change and that stops the PH from dropping.

My Question:
Should I add nutrients to the reservoir after this mid week full reservoir water change? Or should I wait until 7 days since the last nutrients change to add the next weeks does of nutrients

1 Like

You say DWC but mention a reservoir: which is it?

Adding daily is pretty common with bucket hydro (DWC) but would replace with more nutrient solution. If in a rez then every couple of weeks. Having a large standing reservoir of nutrient solution will resist swings in TDS and PH.

You should be shooting for around 900 ppm in veg, 1,100 ppm in flower. Pictures would be helpful and filling out a Support Ticket will pin down a lot of the variables:

COPY/PASTE the below list into your forum post.

Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so; Or post
NA (non applicable)

-What strain, Seed bank, or bag seed (photo or auto)
-Age of plant
-Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
-Vessels: Type and capacity of container (fabric, plastic, etc)
-PH and TDS of Water, Solution, runoff (if Applicable)
-PPM/TDS or EC of nutrient solution if applicable
-Method used to measure PH and TDS
-Indoor or Outdoor if indoor, size of grow space
-Light system List brand and wattage/spectrum
-Actual wattage draw of lights
-Current Light Schedule
-Temps; Day, Night
-Humidity; Day, Night
-Ventilation system; Yes, No, Size
-AC, Humidifier, De-humidifier,
-Co2; Yes, No

If growing Hydro some additional questions:

-DWC? RDWC? Autopots? Ebb and Flow? Other?
-Distance of liquid below net pot (DWC)
-Temperature of reservoir
-TDS of nutrient solution
-Amount of air to solution

Always try to upload a clear picture in white light of any issues you may have to allow the community to assist you.

3 Likes

Thanks @Myfriendis410 ! The plant is in a 5 gallon DWC system that is topped off with 3 gallons of water daily now.

So it is okay to add nutrients back into the DWC bucket after a full water change? I just wanted to make sure that I didn’t causes nutrient burn.

And I am following this feeding schedule:

-What strain, Seed bank, or bag seed (photo or auto)
ILGM Blue Dream Autoflower
-Age of plant
60 days since germination
-Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
Hydroponics
-Vessels: Type and capacity of container (fabric, plastic, etc)
5 gallon DWC bucket topped off at 3 gallons every morning. Adding about 1 gallon of RO water a day
-PH and TDS of Water, Solution, runoff (if Applicable)
PH is staying around 5.7
-PPM/TDS or EC of nutrient solution if applicable
Currently PPM / EC is near zero because I just did a full water change with RO water
-Method used to measure PH and TDS
Pens
-Indoor or Outdoor if indoor, size of grow space
Indoor tent that is about 3ft x 3ft
-Light system List brand and wattage/spectrum
200w Blackdog LED
-Actual wattage draw of lights
200w
-Current Light Schedule
24 hours light
-Temps; Day, Night
77F
-Humidity; Day, Night
45 RH
-Ventilation system; Yes, No, Size
Fans pulling a good about of water in and out to keep humidity low in flowering
-AC, Humidifier, De-humidifier,
Just air circulation and a space heater
-Co2; Yes, No
no
If growing Hydro some additional questions:

-DWC? RDWC? Autopots? Ebb and Flow? Other?
DWC
-Distance of liquid below net pot (DWC)
Topped off at about an inch below the net, but the water level falls significantly each day and adding Hydroguard
-Temperature of reservoir
68F
-TDS of nutrient solution
-Amount of air to solution
6 watt pump pushing into airstone for oxygen in the water




3 Likes

And with the midweek (3.5 days since last full water and nutrient change) full water change, what amount of nutrients should I add? Should I add the same amount that I did 3.5 days before, now that I fully removed all that water? Or, should I add a lower amount of nutrients and then go back to the amount in the weekly feeding schedule once it has been the 7 days since last full feeding

1 Like

Okay; let’s say your target solution TDS is 800 ppm. Due to the fact you are turning over your entire bucket almost daily you might as well replace with 800 ppm nutrient solution. You could monitor TDS in the bucket and adjust your mix (either dilute or concentrate depending on how plant is feeding) but essentially you aren’t doing a rez change at all but a reset/cleaning.

This is the problem with bucket hydro in that you don’t have any supply in a reservoir to replenish liquid as it’s used.

It looks like you are doing a good job of keeping things going well and so far is a pretty plant: good job! But you might consider upgrading to a standing reservoir if you continue with hydro.

Personally I like the option of being able to walk away from my grow (travel) for a week if needed and not need any attention. You can achieve that with the addition of a reservoir (and probably a chiller).

I probably wouldn’t worry about doing a reset with the high turnover of liquid in your setup: just mix and replace as needed.

1 Like

@HerculePoirot I have found that some plants will drive the PH low and some don’t mess with it much. I fill with the same strength of nutrients if needed during my 7 day changeout schedule. Nice grow

Thank you! It’s with your support - and this community - that I have been able to finally get to flowering stage. This will be my first harvest in about 4 weeks.

I will look at adding a standing reservoir. I do currently run a chiller in and out of the DWC bucket.

I thought I read somewhere about salt buildup in the water in flowering and how that could cause PH to drop. So that’s why I started doing the half week full water change in flowering. Because it seemed like that was the time when the PH just starting dropping down fast.

Thanks! This is my first successful grow of ILGM Blue Dream Auto, I tried with a couple seeds over the past few months and learned from a lot of mistakes. :slight_smile:

1 Like

that’s how you learn…mistakes make you a better grower…

2 Likes

Amen @Retiredoldguy my friend I’ve screwed up so much and not on just cannibas plants

2 Likes

It’s pretty normal for PH to change over time: that’s what PH up and down are for lol. Running RDWC, you will do a rez change every couple of weeks but you have complete turnover of your nutrient solution daily.

Folks running bucket hydro do have issues with this change in volume and it only gets worse as the plant matures. Personally if I were doing DWC I’d modify a 29 gallon yellow topped tote to hold one plant: that gives you a lot more stable solution. Adding another same sized tote as a rez will give you at least a week before you need to add anything.

Very common if you water is not moving around in reservoir ?



Either will work , its just which one can you afford ?

Thank you!! That’s super helpful advice. I will look into you RDWC suggestion and the two 29 gallon tote idea!

1 Like

thank you for the advice, i didn’t realize it was related to the water not moving as much :slight_smile: