Refugiums, Macro Algea and Nitrate Reduction

I have a 75 gallon Fish only Salt Water tank. The tank is filtered using a large wet/dry (6 gallons bio balls), a protein skimmer, a uV strilizer and a recently added Refugium. The tank is fully stocked with a total of 8 fish. List of fish and other general data on the tank is listed below.

I added the refugium to bring down nitrates. The refugium is one I bought on Ebay 12 inches by 4 inches by 12 inches (long hand on version). I pump water from my wet/dry sump to the refugium using a rio 600 (the refugium is mounted on the sump not the tank). In the refugium I have caulerpa ( a little grape, a little feather, and a lot of Razor) and Chaetomorpha Sp. (aka Spaghetti or Brillo Pad Algae). I light the refugium with a 13 watt Jalli light.

The refugium is running for 3 weeks now and to my surprise the nitrates do not appear to be going down ! Can anyone tell me why ? My local fish store claims the refugium won't work, but I've read too much material that says it should... Help ! See more tnak info below.

- Volitan Lion
- Clown Trigger
- Niger Trigger
- Dog Faced Puffer
- Yellow Tang
- Blond Naso
- Cuban Hog
- Greem Birsd Wrasse

-Ammonia and Nitrite are always at 0,
-PH always tends to drop buy is maintained using PH buffer,
- 20 - 25 gallon water changes every 4-6 weeks
- Nitrates at about 40 PPM these days

[Matt Rogers]

Those fish are eating machines, I'd do water changes a little more often if you can.

What kind of sandbed do you have? How deep is it?
Do you have LR?

[inwall75]

Your ammonia and nitrites are at zero because of the bioballs. *They are excellent for highly stocked FO tanks. *They oxygenate the water and they have so much surface area that they can house tons of bacteria for the first 2 parts of the nitrogen cycle. * The water goes through and the bacteria turns the ammonia into nitrite which is then turned into nitrates. *However, their very nature means they cannot house anaerobic bacteria. *As a result, there is nowhere for the nitrates to go but back to the water column.

In addition, As Matt said, a number of the fish in your list are heavy ammonia producers (and messy eaters). *You are having a problem because of this plus the nitrates from your bioballs. *

The refugium will help keep your nitrates from rising but you might need a bigger refugium or you might need a DSB or you might need to do waterchanges more often or you might need to see which macro's are growing the fastest in your fuge and use more of that macro.
I have personally had much better luck for nutrient export with grape caulerpa even though most people like chaetomorphia because it doesn't go sexual. *

What type of substrate do you have and if it is crushed coral or rough aragonite, when was the last time you vacuumed it?

[Matt Rogers]

inwall - i made a spelling edit on that first sentence. you had nitrates, but you meant nitrites.

Thanks for the quick responses....

The reason I am surprised not to see a reduction is that the tank is set up for 2 years now. Nitrates have been at 40 PPM and never gone above that level, so it stands to reason to me... that if the refugium was doing anything, I should see a reduction ! Why aren't I seeing it ?

To answer the q's you asked: I have a pink somoa sand base in the tank (only about 1 inch deep), Kent Mud in my refugium, no live rock, lots and lots of dead coral and shells.. (looks really good, the nices fish only tank I've seen if I do say so myself !)

Could the issue be that I have too much algea in the refugium ? It is loaded... if I harvest some, would that promote greater growt and consumptrion of the nitrates ?

[Craig Manoukian]

If those fish grow to maturity, your tank will almost definitely be overstocked. How many inches in fish do you currently have?

The general rule of thumb is 75 inches of fish, 1" per gallon, and those fish can easily eclipse 100 inches when fully grown. The feeding requirement for those fish can also elevate nitrates as was previously mentioned.

Has the macro algae grown or increased in size during the last three weeks? If it is growing it is using nitrates and it may take some more time for the macro algae to root and get established. I would continue to wait and see

I agree with Matt that you may want to increase the frequency of your water changes to export the nitrates. Continue testing and monitoring as it may take two or more months for your system to stabilize.

[inwall75]

If you have a refugium and you don't harvest any of the macroalgae's, then they absorb as much as possible and then 'go sexual' and release a lot of the nutrients to provide food for their babies.

I suspect that this might have happened.

When trimming caulerpa's, pinch to cut and hold for a second. Then remove. You still might need to run carbon for a day as they will release gelbstoff (yellowing agent).

I recommend trimming often.

[Craig Manoukian]

Curt,

The refugium has only been set-up for three weeks. How often should you trim the macro?

[inwall75]

Basically growth determines how often it should be trimmed. The mere fact that it the refugium is totally full means that it has absorbed a lot of nitrates and phosphates (or that too much was put in to begin with). If it gets too thick, light can't penetrate and you will have some die (instead of going sexual) and release the phosphates and nitrates.

I think that good pruning practices go a long way toward keeping Caulerpa from going sexual. If pruned back regularly, there is less volume of algae which need nutrients - it doesn't have to 'share' with a larger volume. Less algae = less food needed = sufficient food for existing algae.

In other words, I believe in using less algae but pruning more often to ensure that there is always new growth and that all macro's are exposed to light.

The only time I ever experienced caulerpa going sexual was when I when I let my fuge get overgrown.

[Craig Manoukian]

Great information Curt, karma to you!