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Ideal water temp

Posted by wordwiz (My Page) on
Sat, Jan 31, 09 at 17:58

We are in the dead of winter and my grow room gets a lot of ambient heat but it is not hot. It doesn't make much difference (until now) because all the seedlings are in a chamber where it stays warmer. But I want to start some toms in a hydro unit and the water now is 20C, 68F. The air temp is 72F so the water will warm up a bit in time.

These are small seedlings that really don't have any true leaves yet, just good roots in rockwool. I figure plants get set outside in May when the soil temp is ~65 and the nighttime temps can drop well below 72 so don't see this as a problem.

Any experiences?


Follow-Up Postings:

RE: Ideal water temp

Hi Mark,

If you are asking what the ideal water temp in hydro is it's 18 to 27 degrees C, or, 65 to 80 degrees F

RE: Ideal water temp

My research has indicated that when plants are in a "vegetative" state, a root temperature of 84 degrees is ideal. I grow tomatoes and strawberries.

RE: Ideal water temp

The reservoir temperature, in my experience at least, works better on the cooler end. If you can get it down towards 68-72F that's ideal because thats the temperature where water can hold the most oxygen.

The more O2 you have dissolved in your water, the better your plants will grow and the less problem you're going to have with algae and other unwanted crud in your tank.

Freemangreens could definitely be right about 84F, but I'll stick with closer to 70F just because you really start to have more chance of gunk over about 73F. I'll risk a bit less growth to have no algae.

RE: Ideal water temp

What really makes a difference is how much oxygen can be held in water and it has upper limits, ie, as water gets warmer, it will hold less oxygen.

Solubility begins to fall off rapidly at 30 C.


RE: Ideal water temp

Got one of those in F for the colonists?

RE: Ideal water temp

Quick conversion to degrees F: double the degrees C and add 30 :-)

RE: Ideal water temp

You can also add OXY-MAX Oxygenator or 35% H2O2 to add oxygen to your res. I forgot to paint my res white so my res temp run between 70F and 75F and my crops are just fine. But I also have four 12 inch air stones in a 27 gallon res of which I only fill with 42 liters or roughly 11 gallons. I swear by H2O2 I use it though out my whole grow veg and fruiting.

RE: Ideal water temp

"Quick conversion to degrees F: double the degrees C and add 30 :-)"

That's only vaguely accurate, since 5/9 is vaguely similar to 1/2 and 30 is vaguely similar to 32. If you don't mind being off by a few degrees 100% of the time it's not bad, but the formula is a bit more complicated than that.

Double the degrees C, subtract 10% and add 32. Or 5 degrees Celsius to 9 degrees Fahrenheit plus 32.

And none of that makes it easy to see the relationship of the curve in the graph to degrees F unless you convert all the numbers.

But anyway, as long as your res isn't colder than say about 62F you should be fine. Below that you can retard growth a little simply because the roots are cold.

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