To overflow or not...

[Mouflon44]

I am planning a large (mostly low tech for now) planted aquarium. My next step in planning my tank is deciding if I should have overflows for removing surface scum or just go with some canister filters. OR can I fix it where I can have an overflow into a canister? From what I've been reading I need to conserve CO2 by staying away from the trickle/bio ball filters, but I also want a way to keep the surface water clean. Anyone?

[125gJoe]

I have an 80 gallon with 2 canisters running and no surface scum.

Canisters provide a 'closed' filtration system with no 'gassing off' of CO2. There is a slight surface movement, so I suppose that helps keep the surface from getting stagnant and dirty..

[The Gipper]

On my 120 gal planted, I just switched last weekend from overflow/wetdry to a canister with no overflow. I originally decided on overflow/wetdry because of a surface scum problem in past tanks.

I switched to canister because I lost tremendous amounts of CO2 during the trickling of water over the bioballs in the sump (could not get below 7.0 without running my 10 lb CO2 at a rate that would use it all up in 3 weeks!!).

Now with the canister, I have no problem with maintaining 6.5-6.6, at literally a fraction of the CO2 usage (I bet my 10 lb CO2 tank lasts 3-4 months or more). HOWEVER, THE SCUM IS BACK!

Within days the surface scum began to form. I do have an open top, and I'm sure there is some level of dust, etc settling in from the room. MY CO2 is around 30 ppm, which I have read on other forums seems to cure the surface scum problem, but not on my tank. I add Fluorish, KNO3, K2SO4 as well as CO2 at recommended doses (Tom Barr). Plants pearl and grow like crazy.

My 30 gal low tech plant tank with glass top(15w NO Fluorescence, no CO2, aquaclear 150 HOB filter, only add fluorish) has NO SCUM and never has. Plants (Anubias sp., Java Fern, Crypt sp.) grow slow, no pearling, but are doing great.

SO... if you go an open top, high tech, watch out for potential surface scum. Aquaclear makes a surface skimmer attachment for HOB or canisters. Plan B is to get one of these (cheapo at Big Al's) and give it a try.

[125gJoe]

The Gipper, thanks...
You are proof (and so am I) that canisters do work very, very well with pressurized CO2! I was involved in a rather 'heated' discussion i the past over the question about Wet/Dry's gassing off CO2.
Canister filters are a 'Closed filtration' system.... There is no "water-fall" effect to 'gas-off' the CO2. It's a beautiful thing!
:)

[125gJoe]

The Gipper, the scum you mention has happened to my tank(s) too. There is no way 'dust' is to blame. In fact, deodorant is much more likely a culprit that dust. ...I know, thinking of that sounds somewhat digusting...but it's possible. If you never reach that far into your aquarium --- I would find that hard to believe! Also, look into any fatty foods you might feed the fish... Food rich in fat might leave a layer on top.

Anyway, I've had the topwater scum problem for a very brief period. Drag a fine mesh net through it - really disturb the scum and the filter(s) will take care of the rest.
Freshwater aquariums should never need a "skimmer".