Using GAC

Shawn_epicurious · Jun 9, 2020

I am using the reactor below for carbon... you can see how much I put in it... I know you saw the poll R2R sent out today. Everyone in there was talking about how short a lifespan GAC has... I was shocked!

I am getting myself ready for an SPS dominant tank (it’s all in my build thread : ) Now I have questions about how I am using this. The GAC I put in there was a premium grade.

1. Should I have used that much GAC in the reactor all at once? Would I be better served filling it halfway?

2. If it is filled correctly, how often does it need to be replaced?

3. I was shocked by people’s comments on the R2R thread today... why does it have such a short lifespan? I really thought I had at least 90 days before needing to change this...? Active carbon gets used in.... a lot... of ways in this world. I never knew it had a short life span...

Spare time · Jun 10, 2020

Using that much at once can cause HLLE if the carbon is a cheaper more brittle kind, increase phosphates, and become saturated with organics with negative charge that leads to the stripping of trace elements with a positive charge if left in there too long. Follow the directions on the carbon packaging as for how much to use and how often to change out.

Skip to 3:50

Randy Holmes-Farley · Jun 10, 2020

I agree that brand is very important, and things like HLLE are a risk.

I'd recommend a high quality, acid washed material like ROX 0.8.

.My recommendation is to only change part of it at once if using that much, especially if also organic carbon dosing as I found the GAC was a place that bacteria liked to grow. I used only a cup or two so in my system with a water volume of about 300 gallons, and only changed a part of it once every 2 weeks or so.

Shawn_epicurious · Jun 10, 2020

I have to read the direction on the container? Well that’s not fair! Lol

I’ll be changing the set up on my rector today. I should have paid more attention in chemistry class 40 years ago : ) I actually thought I was being smart in how I set it up... that dude on the video called my setup “lazy.” Wow.

Anyway, this is why I love R2R! You guys are the best! Thank you!

Hydrored · Jun 10, 2020

I use ROX .08 at half the recommended usage in my 210 changed every 2 weeks-

here is a calculator

Aquarium and Reef Calculators - Bulk Reef Supply

Bulk Reef Supply - Saltwater Aquarium Supplies for Reef Tanks

www.bulkreefsupply.com

Shawn_epicurious · Jun 10, 2020

Hydrored said:
I use ROX .08 at half the recommended usage in my 210 changed every 2 weeks-

here is a calculator

Aquarium and Reef Calculators - Bulk Reef Supply

Bulk Reef Supply - Saltwater Aquarium Supplies for Reef Tanks

www.bulkreefsupply.com

I’m not going to lie, when I set this reactor up, I thought... it’s just carbon. If a little is good, more is better. Oddly enough, I don’t think that thought process has ever really worked for me. Yet... I still do it. Smh

That calculator is awesome! It recommends 1.25 cups. Thankfully I have only had that reactor going this way for less than a month.

Dkeller_nc · Jun 10, 2020

It's a little tough to tell from quickly scanning your build thread to see what you system size is, and your carbon reactor's size. You may have mentioned it, but one reason that I've been off the forums for a few months has been getting overwhelmed by work because of the pandemic (we make SARS-CoV2 tests), so I couldn't spend a lot of time going through it.

But, some tips. As you've noted, GAC in an aquarium system is rapidly saturated with organic compounds. Within a few hours in some cases. However, that's not the whole story.

There are many different organic species in aquarium water (whether salt or fresh). Each of these has a different tendency to adsorb to carbon (sometimes termed "affinity" in the chemical engineering world). Even though the carbon reactor might be almost instantly saturated with easy-to-adsorb chemical species from the aquarium water, they can subsequently be displaced by organics that have a much stronger affinity for the carbon matrix. This is why the principal reason for including carbon in a reef system is removing water-coloring compounds that slowly build up over time. These compounds have a very high affinity for a carbon matrix, so it really doesn't matter if the carbon initially gets saturated with other compounds when it's first put into tank water - the carbon will still prevent the tank water from yellowing for a month or more, depending on how much is used.

Shawn_epicurious · Jun 10, 2020

Dkeller_nc said:
It's a little tough to tell from quickly scanning your build thread to see what you system size is, and your carbon reactor's size. You may have mentioned it, but one reason that I've been off the forums for a few months has been getting overwhelmed by work because of the pandemic (we make SARS-CoV2 tests), so I couldn't spend a lot of time going through it.

But, some tips. As you've noted, GAC in an aquarium system is rapidly saturated with organic compounds. Within a few hours in some cases. However, that's not the whole story.

There are many different organic species in aquarium water (whether salt or fresh). Each of these has a different tendency to adsorb to carbon (sometimes termed "affinity" in the chemical engineering world). Even though the carbon reactor might be almost instantly saturated with easy-to-adsorb chemical species from the aquarium water, they can subsequently be displaced by organics that have a much stronger affinity for the carbon matrix. This is why the principal reason for including carbon in a reef system is removing water-coloring compounds that slowly build up over time. These compounds have a very high affinity for a carbon matrix, so it really doesn't matter if the carbon initially gets saturated with other compounds when it's first put into tank water - the carbon will still prevent the tank water from yellowing for a month or more, depending on how much is used.

Wow, you are right about my build thread... I didn’t realize that : ( It is a 200 gallon tank.

Every time I think I “know” something about this hobby, I get smacked around! Thank you for this write up. : )