Is My Air Pump Big Enough For My 35 Gallon Rez?

GPH is a meaningless statistic on air pumps for hydroponic growing purposes.  What counts is WATTS!  Watts are where it's at.
 
Flip your pump over and read the fine details. 
 
You want a minimum of 1 watt per gallon of nutrient solution.   2 watts per gallon is ideal.   This is the backbone to hydroponics (oxygen in the root zone) so you DO NOT want to skimp here.  You want about 60-70 watts of air pump power for a 35 gallon reservoir (assuming you don't fill it to the rim).   Yes, that's going to be a small investment in air pumps!   I recommend the Alita brand, as the best I've ever used. 
 
Note, you must also keep your nutes temp below 70F in a DWC setup.  If you can't do this, another method might be better for you.

 

No man, watts mean nothing. The watt count is only how much electricity the pump uses. This has nothing to do with the amount of air that comes out of it. You have that backwards. The amount of air that is pushed through the water is what you should be concerned about, not how much electricity it uses. Some pump designs are more energy efficient than others
 
The amount of air I always recommend is 1 litre per minute for every 2 litres of nutrient solution. 
 
951 gph if that's US gallons it equals to 60 litres per minute and so is suitable for anything up to around 120 litres. Which in US gallons is about 32. So yeah that's a pretty good match in my opinion

 

Hi Gold, I see that we finally found something that we don't see eye to eye on!   I do know for a fact that we can agree that a properly oxygenated root zone is one of the most important factors in a hydroponic grow.   
 
Of course every pump will work at a different efficiency, making watts not an equal spec to compare pumps by.  However this is also true of using the measurement of gallons per hour.  All things considered, I've found the measurement of watts to be far more accurate and safer to use than GPH.   GPH is a measurement that's highly subjective, whereas watts can actually be measured and tested using simple equipment, making it a more objective measurement to use.
 
Any modern air pump is going to be of sufficient efficiency to compare with others using a similar power draw for our purposes (which is why I quote a range.  1-2 watts per gallon, to cover any gap).   Watts is a measurement of the amount of power used by the pump.   That power is converted to one of two things, air being pumped out, and heat.   Unless you have a pump that's running HOT (which indicates a problem with that pump), then the measurement of watts is the best basis of comparison because it is indicative of the potential power of the pump.
 
The problem with comparing liters/gallons per minute is that it doesn't take into consideration the head pressure at the pump.   The longer the tube, the more bends in the tube, the size of the tubing, the number of fittings, the deeper into the water the tube is inserted, the less efficient the pump will run, and the less air it will output.  The GPH measurement is subjective to marketing hype, and could be over estimated.   Even if it is not over estimated, it's going to be stated as measured at the outlet of the pump, rather than with a particular head pressure resistance. 
 
I trust Gold's opinion that his calculation will infact work great, I'm not arguing that at all.   GPH is far more subjective to interpretation than the actual power draw (in watts) of a pump.  It would be interesting to learn the power draw of the pump you choose, whichever method you use.  I'm sure it will fall within range of my recommendation, too.  If you're looking at the pump I think you're looking at, it's a 35W pump, which falls squarely into the MINIMUM size pump I recommend for your 35 gallon reservoir.  But two of these would be even better.   Don't forget that you'll need bubbles at the plant sites, too... you must calculate the volume of nutrient solution at each site.  
 
That said, you may choose to measure your pump by any means you see fit, but your pump, or sum of all pumps doesn't equal at LEAST 1 watt per gallon of nutrient solution, you're going to have problems.
 
Keep in mind that the gas exchange in your nutrient solution is by far one of the most important aspects of growing DWC, and you almost can't over-do the amount of bubbles you provide.   If you underpower it, you'll be sorry.   
 
Finally, don't forget that you'll also need to aerate the plant sites.  You can use individual pumps for these sites, or tap off your one big pump (creating a head-loss) to churn the water under the roots, too.   But you need to calculate the plant site, and the water in the pipes, in addition to your reservoir. 
 
FYI, you won't need any luck to grow, once you learn the ropes! 
 
Cheers,
Past

 

 
Hi Guerilla,
 
That's a great story man, Gold always has excellent advice!    Growing hydro is a trip, when you convert from dirt.   Utimately, we're delivering the exact same things to the plant as in dirt, but we use different methods to do so.  Instead of letting your soil dry up a bit, we have to deliver bubbles to oxygenate the root zone.   Different techniques to accomplish the same result. 
 
DWC is a GREAT method to grow in, as long as you can keep the critical variables (that are particular to DWC) in check.  In any hydro setup that single most important variable is dissolved oxygen.  DWC, in particular, you can maximize your DO by increasing your bubbles, and keeping the nutrient temps low (below 70F, 68F is ideal).  Other hydro systems, this isn't a worry, the oxygenate the roots by other means.  So DWC in particular has these specific traits that you have to learn about, to be successful.  
 
It sounds like you're learning along the way.  I LOVE that aspect of growing, and that's why I LOVE growing.  We all make mistakes, and as long as we learn from them, I think mistakes are a positive experience. 
 
I would suggest throwing both of your 45 watt air pumps in there!  one for plant sites, one for the res, and you'll be happy you did. 
 
When I built a RDWC system, I added a water chiller, which made a HUGE improvement to the grow.  However, all the extra gadgets to clean go against my inherently lazy sense of being, so I have to use a less labor intensive method to grow.  I use flood and drain tables currently.  These are great because I have zero DO problems, and I can leave town for two weeks and come home with no surprises.