Lowering Phosphates with GFO

GFO has been a popular choice to reduce phosphate in reef aquariums for a while now, but many people who use it don’t even know that it has the ability to be recharged. This is true and the only chemicals required are sodium hydroxide and some clean water. I use 0TDS water, but I have not tested with different grades of water. GFO or Granular Ferric Oxide can get expensive to run and in my case I hate spending a lot of money, so I got some sodium hydroxide and decided to try it myself.

Recharging GFO

After having a great first attempt with recharging GFO, the only thing I could think about was all that product I threw away in years past that i could still be using. I got over that quick considering i had a good amount of exhausted media i had been saving. The only thing i had to do was to get some sodium hydroxide. Lucky for me i work with a lot of chemistry at work and had more than enough to try. Im sure getting it other ways is easy. Many products such as drain cleaner are actually just sodium hydroxide. There are sulfuric acid drain cleaners, so make sure you know what the makeup of the product actually is. The best way to find out is to just look up the MSDS. Sodium hydroxide is a salt that when dissolved in water becomes very basic. This means the PH goes up to the higher limits of the PH scale, around 14. Sodium hydroxide’s basic nature is the reason why it recharges the GFO. This is due to the OH ion attached to the sodium. This ion is the main workforce when it comes to charging the GFO.  The OH breaks the bond of the GFO and phosphate. This is how the phosphate goes back into solution so you can rinse it away.

My First GFO recharging experience

The first time I decided to try and recharge GFO was a few years after I had read an article about it. Soon after I did what every modern person does today and looked it up on the internet. As i was researching the process i stumbled on a video with a pump recirculating the NaOH solution through gfo in an up flow type reactor. I believe that to be a bit overkill, although it would probably save a bit more GFO, but I kept thinking back to my thought that this must stay cheap, that’s the point. So for the most part i followed the ideas i read about and ended up mixing the solution to about 1m this means in 1 liter of water there is 1 mole of NaOH. NaOH has roughly 40 grams of dried mass in 1 mole. I added the solution to the gfo in a 5-gallon bucket and then forgot about it and left it in the solution for much longer than what i had previously read, which was about 24-48. Honestly i must have left it in the bucket for a week or 2. I still decided to go on with the experiment and rinsed it a few times with clean water. I then spread it out on a flat surface to dry naturally. Once it was dry I bagged it and took it home to try out. Once home I rinsed it with ro water (kind of funny we dry it just to get it wet again). Then put it into my reactor. I did remove the effluent hose from the tank and placed it into a bucket so I could test the effluent water. It did come out with a high PH about 9-10, but only for a gallon or 2. I came to the conclusion I needed to rinse it better next time, maybe even use as ph probe while rinsing so I could monitor the PH. Once the PH was right I tested the phosphate content, 0.00ppm. I was happy. I put the hose in my tank and let it circulate. Using a reactor works great, it lets the GFO tumble nice and gently, while very efficiently stripping the water of PO4. I was impressed the first time I found out that using gfo in a reactor strips the PO4 down to 0.00 in one pass.



Learning from my first GFO recharge

The next time I recharged a batch of GFO I wanted to try my own way, which isnt much different. I decided against mixing the solution to 1M and wanted to try a more concentrated solution. I chose to do this because I did not want to let it sit in the solution for 2 days. My tank was getting close to 0.10ppm and I needed gfo quick. I mixed it up to around 3-4m and mixed the GFO in the solution for about 20 minutes, that’s it. Once i felt the GFO was mixed thoroughly I then began to rinse. Since the solution of the NaOH was quite high it took a good amount of water to rinse the media. I did end up using a ph probe while rinsing to watch the ph. I rinsed 1 gallon of media with around 10-15 gallons of water. I also did not let it dry naturally this time I put it in an oven at 250F. When i  put it in the tank I had no problems with either PH or phosphates. So finding out one doesnt need to let the GFO sit in the solution for 48 hours was awesome. I recharge my own DI resin so going from recharging that to this is a piece of cake. I do recommend buying the high density GFO It seems to fall apart a lot less than the other stuff when it comes to the recharging process. Overall if you decide on recharging GFO don’t worry and don’t over think it. Use the proper saftey precautions and overall don’t be dumb. The process will treat you well, and at the end you’ll save yourself some money.