RDWC nutrient & top-off questions

Hey all,

Moved from NFTs to 8 pot RDWC in 5x10 tent. I have all other inputs tighly controlled and measured except nutrients I feel like. My ratios seem to be screwed up even if I try to go only half of suggested Canna chart.

  • Steady 0.9-1.1 VPD
  • Chiller and water heater to keep water 18.5-19c
  • Air temps 25-26c during day 22c during night
  • 480 ppfd all accross tent
  • PH fluctuating between 5.7-6.2
  • Veg week 3 EC 1.0 dropped to 0.9 after running for 4 days (some 150 liter system) PH keeps going up every 4 hours and plants consume some 7 liters a day

I run Canna Aqua with Rockwool only. My tap water is 110, I have added Calmag until I hit 250 ppm, then A, B, Rhizo, Cannazym (CZ starting week 3 and RZ ending week 4)

Now come my two questions:

  1. Without water report, would it be safe to say I can drop CalMag 250 > 200, so just add 90 to base rather than 140 ppm.

  2. My system is hooked up to 280 liter tank with float valve. For now any remaining water I have after change. After water change I see how much in the tank and double the amount with fresh water. Then leave it as top off. I am trying to figure out a sufficient method that will not cause salt buildups but doesnt require heavy math.

  3. What might be causing the issues seen in pictures (and slow vertical growth)?

Any tips are appreciated!


morning @santsi looks like you have a big grow going here and nicely setup… I am happy to help you with some of you questions…For CalMag I add 2 tsp to every 5 gallons of distilled water…I don’t use external reservoir…how often do you plan to do a complete drain and refill??

the leaf issue looks like ph swings and the other pics looks like she is starting to flower…


Are you sure the Canna line needs the calmag? In a hydroponic grow it’s customary to add calm for peace of mind but a lot of base nutrient will cover everything that is needed. I’m not sure if this is general practice with canna aqua line but thought I would ask. How much per liter or gallon to get to the 250 ppm?

This is really cool, but makes you predermine what is going in. I would probably just do hand top offs for a while so you can test your solution before and after. If you have roughly 150 liter of solution and using 7 liters per day you have a good buffer. Also wondering how often you are doing completely change out of solution?

Ec of 1.0 may be a little low for plants this far along or potentially the swings on ph.


I used 37 ml (Google says 5x that for teaspoon) to 100 liters / 26 gallons of water. And my water has 110ppm (x700) base value.

This is along the guidance from Canna CalMag chart, and even on the low end of it. But I have been thinking it is still too much.

I have so far changed reservoir water once every two weeks as plants havent used that much but as the speed ramps up considering best process between top-up and 7/10 day change to minimize nutrient issues.


Absolutely not certain. I have followed Canna advise to raise water EC to 0.4 before adding Nutes but I feel like this adds too much CalMag. And so I reckon I am overusing it. So far I figure I will minimize the use on next water change on Tuesday and see the effects. This also leaves room for more A and B nutrients.


as @dbrn32 mentioned with tap water and your other nutrients calmag may not be necessary…also good advice on how to track your nutrients in a multi plant system…


also most growers will say use half or less of what the nutrient company says to use…less is best until you get your groove on…


That is what I am already doing. But I reckon I with CalMag I need to use half of the half…!


are those autos…

Nope these are clones from a friend. He actually also pointed out that some growth on the plant looks like white pistils but it hasnt had light trauma or such that should have triggered any.


ok then not in flower just showing her sex is female…
something to consider in hydro is that during veg phase when she wants more Nitrogen over Potassium and Potash she will make the ph head towards 7ph and when in flower phase and she wants more Potassium and Potash over Nitrogen she will make the ph head down to 4ph…this is something that happens naturally as she takes in NPK at different levels/phases


It was actually calcium deficiency causing those rust spots, I reckon it was just due to underfeeding as was suggested. After increasing EC to 1.2 it dropped to 1.0 in one day due to heavy drinking. This week we are going 1.3 and plants seem to be loving it.

New problem has arised though as the plants have grown bigger and are pushing humidity over 65% . The grow space is 5x10 tent and it sits in cold garage (I got two electric heaters on opposite side for if needed) that is not sealed perfectly. Some cracks at the wide doors etc.

I have exhaust running through carbon filter and then to behind of the dehumidifier that sits in top corner of the lung room (maybe 8x14 size). This is because I live in cold climate and dont want to exhaust outside during winter to avoid bringing too much cold air in rapidly…

The dehumidifer is Wood’s Powerful SW42FM Dehumidifier -Made in Sweden and can remove 15-25 liters a day. It runs on maximum settings non-stop but doesnt seem able to control the grow room humidity sufficiently.

Exhaust goes through single 125mm pipe with 420m3/h fan pulling from the tent and hitting the carbon filter before dehumidifer.

  1. Does not changing the filter inside affect performance negatively? I havent done that.
  2. Should I consider moving this unit inside the grow tent (will be very difficult)
  3. Should I consider upgrading to a bigger machine? (this unit cost some 500 new, proper bigger ones seem to cost 800-1000.
  4. Should I consider upgrading the exhaust pipe and fan to push air out of the tent more rapidly to dehumidifer (I doubt that).

I send some new pictures soon.

And the relevant pictures.

Turning to flower after a week from now.

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Moved the exhaust to push outside not indoors. Now dehumidifier is able to control lung room humidity sufficiently without issues. Case solved!

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3 weeks in flower done


Killing it brother… :index_pointing_at_the_viewer: :muscle: :green_heart:
:v: :sunglasses:

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Closing on week 5


I got noth’n to say… just try’n ta get my chin off the floor. :astonished: :star_struck: :heart_eyes:

I don’t know how many folks notice, you’re the first person I’ve seen who uses a chiller and heater to control water temps. Spot on growmie!! It’s much easier to maintain a consistent temp with heat than refrigeration. (I have some injection molding experience)

Holy frijoles what a grow!


morning @santsi I noticed you have the original ACI fans…did you know there was a free upgrade and you keep the old fans …


I didn’t, I’ll be on the phone this morn’n!