Just thought I'd share my impromptu breakdown of last night because it pertains to the big-for-the-future pump vs. right-size-for-your-tank pump purchase decisions that have been discussed lately.

Background: Many people will be shopping for a return pump for a smaller tank and decide something similar to the logic of "I need 250gph, but it's much more economical to get the 750gph pump and just throttle it back. That way when I upgrade my tank, I'll be ready." The drawback is that if you run a high calcium system, a highly throttled pump (especially a submersible such as the ubiquitous Mag) will impart more heat to the water it pumps as well as the surrounding water. The warmer water precipitates/plates out calcium faster. Once plating starts, it progresses easier as well. Inside the pump, the increased friction causes still more heat.

I have a Mag 7 on a 25g tank that was throttled to about 1/3 flow. The return to my tank failed to produce much after I had turned it on following a feeding, so I cleaned the pump and got no change. Turned out that not only did the pump get full calcium, but the return hose (5/8" tube) started plating calcium from the heat as well. By the time I washed it out, it was as if someone had filled the hose 1/2 way with corn flake-shaped bits of calcium. No exaggeration.

Something to consider if you're going to set up a fixed PVC plumbing return and use a "much larger than your current tank needs" pump. Cleaning this flex tubing was a pain, but it would have taken days of vinegar soaks if it had been rigid PVC with an elbow or two.

Great information George. I think that goes back to the K.I.S.S. principle that I use on my tank. The less you add, the less problems you should have.

the key to oversizing a pump is not to place the valve directly in-line with the return. instead, a T with a valve should be added that bleeds off flow back into the sump, so the pump can always run at full throttle, thus reducing heat and other low-flow associated troubles, such as pump wear.

just what i was going to say Greg

Here is another question/thing to think about. Wouldn't a bigger (over-sized) pump produce more heat than a similar smaller pump?

I am going to order a couple of Tunze Nano Streams to replace the powerheads in my DT. They will pay for themselves in 1.3 years just in energy savings over the powerheads. I think that the payback period will be about half of that when you consider that my chiller won't run as much. And, in the summer that means that my home AC won't run as much.

We have had unseasonably warm weather. Right now it is 77 in the house and my chiller is running. It kicks on when my tank goes above 82. I have three 70 watt pumps (return, skimmer and one in the DT) and another 60 watt in the DT. My lights just came on so all that heat is from my pumps.

the question is very brand specific carmie, frictional generations from bigger moving parts can be a very open topic. where everyone can meet in agreeance is that every pump of any make/model will contribute their heat soak to the water in contact with it. i hear where your coming from, i dont even need a heater anymore cause the output of my new 8000lt/h pumps. the others who have used the tunze nano's can speak for your new investment.

As for the previous question the G brought up, id say that unless your using a real small tank, extra current isn't a problem if you can de-fuse the intensity of the returns. Hell ~ even plumbing them to break the water surface into a rolling surge would be an option, slightly more evap, but you cant have your cake & eat it as well. this is what i prefer to do, even with the girls, its orsome when you have that extra energy & your disposal. Even if it means modifying your game plan at the start.:up:

I was thinking that as you step up in size the pumps draw more watts and that would make more heat. If I understand what you are saying the larger wattage pump might produce no more heat because it may have less friction??

Anyhow, those Nano Streams only use 7 watts of power compared to the 60 and 70 watts the powerheads I am have now use. There is a considerable savings in watts even if there is no difference in heat produced. :) So, I can still justify them. :D

ive had smaller pumps that draw larger payloads in the watt department than bigger ones & in the same breath turnover less & generate more heat & noise. its all in the design in my opinion. your drop in watts is impressive to the new tunze units. what do the nano streams push an hour?

They are rated at 660 GPH. Tunze Turbelle NanoStream Pump 6025 - Marine Depot - Marine and Reef Aquarium Super Store (http://www.marinedepot.com/md_viewItem.asp?idproduct=TZ1211&idCartRow=3789871&isKit=0)