https://www.walmart.ca/en/ip/tetra-100-w-heater/6000187907711
So a unit like this will keep the water around 25 C. My question, would i be better off with this or with my cold water? I think my water is between 10-15 C. It is really cold to the touch so I have concerns that’s causing issues.
If your res is fairly big it will take a long time for that to heat the water up .
When it gets too cold I usually just add hot water to bring the temperature up a bit.
what is the prescribed temp supposed to be? I have run colder than i like to hotter than i like i was just wondering as this came up on another board and had me wondering i am sure it ties back to dissolved oxygen. But does that matter when growing in top drip rockwool where there is plenty of o2 in the root zone?
From what I’ve seen on google, the ideal temp is 20-23 C and you don’t want to go higher than 30 c. It sounds like around 15 C the plants start having issue absorbing the nute and they stop at 10 c. Anyone feel free to correct me if i’m wrong 
Ideal water temps for hydroponics are between about 20C - 22C.
There are two different things going on here that need to be balanced out.
BUT
I personally would try to keep temps to a max of 21C with a target of 20 C. Or as close as you can.
If your temps stay higher, you may want to consider adding bleach in low doses every 3 or 4 days. You want around 2 - 4 PPM of chlorine, so its a low dose as a preventative.
I got a 300W Jäger/Eheim aquarium heater in my tank, it’s go down to 19C degrees.
IME you never wanna go over 23 C degrees on your water temps, the oxygen lvls drops and all sorts of anarob crap will have a better foothold and risk to cause root rot and what not.
I keep my res around 19-20 C
Tetra makes some all right quality, but if the lowest heat setting is 25C I would look for another brand.
Jäger / Eheim have good thermostats and they can handle to be fully submerged, I have units that are 10-15 years old and still running!
If a 300W unit fit’s your res, I would get that and not a 100W. The bigger the unit, the shorter on time to hit an even temp.
I second that. Around 20°C seems like sweet spot to me. There comes a lot of problems when temperature of medium raises above 25°C so cooling is more important topic to me in summer.
Long time ago I’ve experimented with 15°C and lower and it led to deteoriation. Basically under 10°C growth slows down. Plant could not switch to flowering properly. Instead strong thick leaves developed as a reaction to temperatures near zero. Flowers practically invisible.
As the temperature decreases, the oxygen gas equilibrium for water actually increases. At first blush it’s somewhat non-intuitive, here’s a graphic:
[1]
Along with the slowing of biological growth (plant and microbes), lower temperatures play a large part in the available DO. Though, going too cool slows and stresses the plant.
Going warm means less DO. You’ll need an increased amount of circulation and an increased amount of air contact. So, a bit of a balancing act.
There is a whole line of thought on aerobic vs anaerobic biology that extends from this as well.
Oh, and to point out, just because the dissolved oxygen graph says something doesn’t mean you are actually achieving those numbers. You have to have a way to ensure that oxygen is being introduced into solution faster than it is being consumed (by the plants and other aerobic biology).
Ditto. That appears to be the consensus temperature for the typical DWC. < 21C and > 17C
Ideal temperature is Fahrenheit. I like to keep my water from 17-20C, but I’ve grown in water up to 26C. This is DWC. Most other hydro systems are more forgiving with higher temperatures.
I find warm water better for rooting. My aerocloners always put off roots quicker in the summer when water is 27-30C. Not sure if that is related to ambient temps and humidity being higher or what. Never got too scientific or experimental with this, just an observation.
Thanks for the correction! I need to up-grade my memory chips to a newer version… 
I have to think twice on that regularly, too.
Similar to the following trivia question:
Without looking, what is more dense (or which is heavier), humid air or dry air?
Hint, counter-intuitive.
I know that one from my years flying RC models and dreaming about owning my very own VeriEze or LongEze. I actually started building a Kitfox at one point, but never got beyond the fuse framing.
Humid air is less dense 
As an American I’ll have to agree! 
you do realize america went metric legally back in the 80’s…
No… & neither do about 400 million others
I’m aware of some optimistic experiments over the last 40-50 years but as far as any national standard adoption, no way jose. 
It’s a logical & reasonable system…no personal objection.
I do jobs at times as a builder and drywaller in canada. Because of our relationship with the usa, the metric system is only really used here outside of those fields. My tape measure is still in imperial and I personally prefer metric after working in it for 15 years in NZ
When I was about 12-13 my friend and I discovered an antique Triumph motorcycle (circa 1928) in a crate in his garage. The story was it was an uncle of someone who’d shipped it back from India. It had an acetylene headlight & mechanical horn, hand-painted license plate, and hand-made muffler(well, more like hand-cobbled)…, which was packed full of nuts by some smart rodent 
.
The old leather seat said 10 to 14 stone which puzzled the f#%$& out of us kids. We had to go look it up & learn something.
So I finally got a thermometer in my reservoir. Anyone know an affordable unit for cooling the water down? In 6 hours the water goes from 12C to 26C…
Just try to aim a small fan at the water surface (if possible), you’ll get at least 4 - 5 degrees decrease. Or employ a small car fridge.
Wait, Im confused. Your water was too cold before, so you added a heater - why is it too hot now?
We need to know how you have this setup. Are you growing in a tent or a room?
What kind of hydro are you doing - DWC or??? Re-circulating or?
Details details details…they all matter 