Evaporation vs Pump Speed

[PotatoPig]

Pardon if this is a known thing… I’m new at this.

Lately I’ve been noticing that evaporation in my tank is noticeably faster when the pump speed is higher and am trying to work out why.

System:

75 gallon tank. 20 gallon basic sump to house heaters and filter sock (I plan on adding more later). Variable speed pump. Lifereef HOB overflow. Soft plumbed with straight drop to filter sock receptacle thing (eshopps holder clipped to side of sump tank).

With the pump at max (approx 300 gph) the evaporation seems to be about 3x the rate than when the pump is at 50% power (using the controller, not sure exact GPH for this).

Any ideas why?

 

[Randy Holmes-Farley]

Might be coincidence based on weather, but if a very thin coating of organic matter is allowed to form on teh surface of the aquarium water, that can greatly reduce evaporation. Tank migth also get warmner with more electricity to pumps.

 

[PotatoPig]

Might be coincidence based on weather, but if a very thin coating of organic matter is allowed to form on teh surface of the aquarium water, that can greatly reduce evaporation. Tank migth also get warmner with more electricity to pumps.

Ah - the film might be what’s happening. The slow turnover from the half-power is a pretty leisurely pace through the sump and it develops a film sometimes, perhaps the same is happening in parts of the tank also.

The change is very noticeable each time I switch up power. My initial thought might be weather, but the rate change has seemed unconnected to humidity over the last few weeks.

I’m not sure the pump heat would impact this much. It’s not a beast of a pump and the heaters total 500W (have two heaters connected to the one controller). I assumed if it’s putting more power in it would just mean quicker peaks and troughs in the temperature as the heater controller turns on and off through the same range.

 

[DCR]

More pump speed means increased power requirement (energy) which is all ultimately transmitted into your water. This will tend to heat the water and increase evaporation. The increased flow may also increase surface agitation. There are likely other factors at work like the relative humidity in your home, but it does follow that increasing the pump speed is going to add heat to your tank.