New DWC System Ph Climbing Wildly

Solved but future reference for others since I couldn't find an answer...

Ph was needing adjustment 4 times a day - waiting until it hit 6.3 or so and then dosing down to 5.2 with a citrus based Ph down. Switched to a phosphoric acid based Ph and now it's stable as a rock. Suspected there were too many bubbles in the pots, nope. Water temp, nope. Didn't rinse the clay balls enough, nope. Simply changed the Ph down solution from citric to phosphoric acid and all the problems went away. Seedlings were really struggling and wasn't sure if they'd make it. After that one simple change, they are off to the races.

Yep. Using the right products from reputable brands is not only an easy way to avoid problems but also helps eliminate possible causes problems

bubblescrogs said:

Solved but future reference for others since I couldn't find an answer...

Ph was needing adjustment 4 times a day - waiting until it hit 6.3 or so and then dosing down to 5.2 with a citrus based Ph down. Switched to a phosphoric acid based Ph and now it's stable as a rock. Suspected there were too many bubbles in the pots, nope. Water temp, nope. Didn't rinse the clay balls enough, nope. Simply changed the Ph down solution from citric to phosphoric acid and all the problems went away. Seedlings were really struggling and wasn't sure if they'd make it. After that one simple change, they are off to the races.

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What brand were you using and what brand did you switch to? If you don't mind.

Was using Flairform Ph Down previously (citrus 500g/L). Never heard of Flairform, was just the standard one at the shop at the time. Switched to Nutrifield Ph Down (81% Phosphoric acid). I'd used the citrus based one forever in my top fed drain to res setup without issue. Something about the RDWC didn't agree with it though. It was a pretty old bottle, so might've been that too. It still lowered the Ph correctly, just couldn't hold it.

They've recovered decently and even took a topping in their stride (3 weeks from seed). Wasn't sure they'd make it they looked so terrible when the Ph swings were going on

bubblescrogs said:

They've recovered decently and even took a topping in their stride (3 weeks from seed). Wasn't sure they'd make it they looked so terrible when the Ph swings were going on View attachment 5192828

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Yeah ph problems can put a hurting on them that's for sure. Let's see this new dwc set up.

Still a WIP DIY just for the veg room. But to give you an idea..

Pots fill through this elbow down the bottom of the pot


I can piece together these little joiners with a filtered drain attachment on top to adjust the water height (it sits in the center of the bucket and drains from the top attachment out the bottom of the pot back to the res with gravity)


These netpots with the raised middle are perfect to slot the drain attachment into. Main benefit is it keeps air right in the middle of the roots as they grow around the raised part


So water is flowing in the bottom of the pot, filling until it hits the drain attachment and then flowing back to the res (with some bonus bubbles as it waterfalls down the tube). Each pot also has it's own air stone though. Also have some top feed rings that drip 24/7 to get things moving quickly at the start.

I built a little table with 4" high legs and to sit the pots on, since it only needs to be tall enough for the return fitting on the bottom of the pot with an elbow attached (I'm severely height limited here - this is under a work bench in the garage). Also drilled a couple of holes in the table so the fittings can squeeze through and pots sit sturdy and flush.

Now I've got it working how I'd like, I'll finish mounting the hoses to the wall so they don't move around when I shift the res. Main thing is those input hoses from the res to the pots needs to be higher than the water level to make sure the pots fill evenly and don't back flow to stress the little pump out. But I'll mount the fan and tidy things up to make it a bit more permanent this weekend.



Seem a reasonable plan?

Don't mind the janky shade cloth, that's my 100w HLG light dimmer since it's only 12" away

Update 4 weeks in and the lettuce is fine now

Looking good!

That looks very chonky!

4 Weeks from germination??!!!!

futurebanjo said:

That looks very chonky!

4 Weeks from germination??!!!!

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Yep 4 weeks from seed. Luckily they are starting to spread out a bit more now a week later

Out of curiosity how much of the pH down where you using? I was looking at the bottle online and I can't believe how little they recommend for pH control! 1-3mL per 100L would leave you with like 0.015grams per liter - that's 0.078mM that's ~25-12.5X less CA than I've read you should use...

Rubisco456 said:

Out of curiosity how much of the pH down where you using? I was looking at the bottle online and I can't believe how little they recommend for pH control! 1-3mL per 100L would leave you with like 0.015grams per liter - that's 0.078mM that's ~25-12.5X less CA than I've read you should use...

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Can't recall, think I used about 2mls in my 40L res - whatever it needed to get the PH back down below 5.5. It dropped it fine, just couldn't hold it. Suspect it was either an old bottle or the bubbles in this system caused it to evaporate out or something. Now the plants are established I barely touch it. Put in 4-5 drops of the phosphoric acid if it's a bit high after res change (i.e. over ph 6) and I don't need to touch it for a week - just adjust the EC now if its misbehaving. Sits at 5.7 all week now

They seem happy enough after their first 3 nights sleep. Going to have to get in there for a chiropractic sesh later though by the looks

bubblescrogs said:

They seem happy enough after their first 3 nights sleep. Going to have to get in there for a chiropractic sesh later though by the looks
View attachment 5204141

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looks like they could use a bit of Mg.

rkymtnman said:

looks like they could use a bit of Mg.

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You reckon? I've heard this strain can be a bit hungry with the calmag. It's only since they've started 12/12 on the growth tips of future flower sites. I just run the base canna nutes (still on the veg ones), could give the calmag a nudge for a few days and see though

I have been drilling them with light too, so that could also be part of it

bubblescrogs said:

You reckon? I've heard this strain can be a bit hungry with the calmag. It's only since they've started 12/12 on the growth tips of future flower sites. I just run the base canna nutes (still on the veg ones), could give the calmag a nudge for a few days and see though

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you are better off just using epsom salt if you only need Mg. 1 gram per gallon along with your nutes usually fixes it right up

rkymtnman said:

you are better off just using epsom salt if you only need Mg. 1 gram per gallon along with your nutes usually fixes it right up

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Thanks, might’ve saved me a trip to the hydro shop! I’ve got a big bag my wife uses for the bath. This do the job (magnesium sulphate heptahydrate)?