Confused on carbon and flow

[MJAnderson]

I started reading the forums about 3 months ago and remembered an article talking about how low quantity and low flow over carbon was best. Recently a thread referencing these articles popped up:

"An Overview of Activated Carbon in the Marine Tank" by James R. Layton
"Granular Activated Carbon In The Reef Tank Part 1" and "Part 2" by Richard Harker
"Activated Carbon For Pure Water" from Water Gardening Magazine

Which was summarized with:

- slow water flow through the carbon works better than water flow around the carbon
- about 1/4 cup per 50 gallons is adequate and should be changed at least monthly

I saw similiar recomendations repeated from Warner Marine, makers of Phosar:

"thanks for the kind words... PHOSaR is great in a reactor too, JDIECK has been running a couple pounds of PHOSaR in his mega reactor with great success. The pellets tend to tumble and spin in a reactor and resist channeling...Basically when you use a media bag it allows a lower quantity of water to flow-thru. This flow rate will lower Phosphate levels slower than using a canister...I like lower water flow in a reactor or in a media bag or canister. High flow like in an overflow chamber or (cringes) inside of a micron filter bag at the end of your overflow pipe will damage the media and grind it to dust. This dust is harmless and will be skimmed out after it adsorbs Phosphates but I'd just rather keep it contained."

But whenever I read a thread on carbon or Phosphate removal it seems everyone runs them in canisters at 250/350gph or works hard to get a ton of flow through carbon. What gives? Is there something I'm not seeing?

I'd like to use as little energy as possible and generate as little heat as possible in my sump and so bought 2 reactors fed with an Eheim pump with 160gph flow split between the 2. Is this not effective?

[Billybeau1]

Boomer likes talking about carbon :D He'll be along in a bit.

[Boomer]

Flow rate is dependent on the BTFP ( Break Through Flow Point). BTFP is a function of the container design that holds the media, i.e., canister filter, box filter, cartridge filter, etc. and even these can be subdivide. It is also a function of the media itself, ie., shape, size and porosity. And the type of GAC it is, Lignite, Peat, Bitum, CS, C-GAC, , etc..

A 100% BTFP is when the fluid ( water or air) begins to find ways to travel around the media, i.e., channeling, chimney effect. Meaning the water/air is taking the route of least likely resistance. This is why VPC (Vapor Phase Carbon, is larger in grain size than LPC (Liquid Phase Carbon), as air is diverted much easier than air due to their fluid density.

Making comments about low flow is better is often just nonsense. Some system can have very high rates of flow and still be very efficient. Thi is why GAC companies speed tons of money on testing flow rates.

Some systems/filter can only work well a very slow flow rates or 30-60 % BTFP, others 100% and still others even way above 100% BTFP, like 200% or more. Pretend that 100% BTFP is gals/hr and a hang on has a pump rate of 200 gal / hr. It should only be running at 30-60 gal /hr. A properly designed canister is running a 100 gal /hr, 100% BTFP but could run at 200 gals / hr and still be very efficient.

Most filters that hang on the back are about the worst there is for this type of filtration, like 30-60 % BTFP. Many of the so called canisters are 100% or even lower, as they do not have 100% positive water flow. Meaning, the internal design allows water to escape, go around the media if the media becomes restricted, plugged. As the media plugs, the water often still leaves the canister at the same flow rate. Meaning, if the media is 100% plugged you still have good flow at the output. One could think of this as a by-pass and a good thing. Me, I do not like this at all, unless such a system used a by-pass pressure switch.

For carbon filtration I like positive water flow canisters. These are where the water almost has to go through the media. It can not escape, water is forced through it, to a point of coarse. If the media becomes plugged the flow rated slows down. If it is 100% plugged there is zero flow rate.

Some bad examples of non-positive flow rate canisters are the Hagen Fluvial's. The water inlet and outlet are both at the top. Water at the inlet is channeled to the bottom and the water then comes up through the media to the outlet. Allot of the water in these can find ways around, so when the media starts to get plugged or even if it is not plugged at all, the water flows easily around the media/containers, due to the internal design of the filter. I do not like this.

The best and most efficient filters, where the water is positive flow, you can have high flow rates, are the old fashion Eheim canisters, such as a and they are still made. In theses all the water enters from the bottom and all water exits through the top. There are no so called baffles, diverters, channelers. The water can not escape and must travel from bottom through the media tro the top. Does that mean there is zero channeling through the media ? No, there is no such thing as zero channeling all media has some channeling as the fluid will always take the route of least likely resistance.

If you want a high flow rate canister for GAC these are the only type I recommend. Leave the baskets out and use good soft very flexible media bags, with as large as posible mesh size you can use.
http://www.petsmart.com/media/ps/images/products/detail/large/September04/lg_7878_3d853.jpg


I'd like to use as little energy as possible and generate as little heat as possible in my sump and so bought 2 reactors fed with an Eheim pump with 160gph flow split between the 2. Is this not effective?

That should be fine

[MJAnderson]

Thanks Boomer.

[Boomer]

Your Welcome :D