Filtering

[Serrateeth_2002]

why do saltwater tanks need protein skimmers while fresh one do not? do carbon take out salt in the water? how to maintain salt levels?

[mogurnda]

>why do saltwater tanks need protein skimmers while fresh one do not?
Because skimmers don't function at neutral or low pH, as are present in most freshwater tanks.

>do carbon take out salt in the water?
No. It is commonly used in saltwater tanks.

>how to maintain salt levels?
Once you have established the correct salinity when the tank is set up, water loss from evaporation is replaced by adding freshwater. Salinity should be checked regularly, especially when you are starting out.

Please buy or borrow and read Fenner's Conscientious Marine Aquarist. It will answer these, and many more questions that you might not have considered, and I guarantee will save you a lot of heartache.

[OrionGirl]

I thought that skimmers were ineffective in FW due to the difficulty in generating the tiny bubbles needed to actually extract the dissolved protiens? The increased osmotic force in SW allows for smaller bubbles, while in FW it's very difficult to get the bubbles small enough. After all, there are FW tanks with high pH, and no recommendation for a skimmer on these.

[mogurnda]

Maybe both, but the way I understand it is that negatively charged molecules stick to bubbles, and that proteins, and many other small organic molecules, have a net negative charge at high pH. The skimmer will be progressively less effective at lower pH. Maybe I'll test this on the Tanganyikan tank this weekend, I'd never thought about doing an actual experiment.

[OrionGirl]

I'd be interested in knowing the results--I don't have any high pH FW tanks, or I would give it a shot.

[Alastair]

OrionGirl is correct about the skimmers. They certainly work in freshwater, they just have to be bigger to provide an equivalent area of air/water interface. Many public aquariums that have the space and funds for large skimmers use them on freshwater as often as on saltwater, with excellent results. So far as I know, pH has a negligible effect on their operation. I suppose it might affect some compounds, because there certainly are compounds that tend to be more ionized at a higher pH, but I think it's the lesser of the two problems.

[mogurnda]

Well, I guess Sprung and Delbeek were wrong. The argument they made was that proteins and other large organic molecules ten to be negatively charged, and will be more so at high pH. Not sure why anions supposedly stick to bubbles better, but you guys are probably right that the issue is probably bubble size and surface tension.
The other piece of evidence against the pH argument is that the technology was developed for sewage treatment (or so I'm told), which is generally a freshwater activity.