Friday, December 5, 2008

How to Reduce Nitrates in Reef Tanks by Increasing Illumination

I believe I have reduced the Nitrate level in my tank dramatically from 25 mg/L down to 0.2 mg/L simply by adding four spiral compact fluorescent bulbs from the hardware store. This post describes in detail all the steps I've taken to reduce my Nitrate level. The chart below illustrates my Nitrate measurements and is annotated with the dates of various things that I tried along the way. Click on the chart to enlarge.

From Paul's Reef

I've been recording my tank parameters since July 1st of this year. I have been most interested in reducing my Nitrate level. The Nitrate level in my tank was staying around 25 mg/L for several months. The level didn't go down by reducing feedings to once a day. Finally, I broke down and added a sump and refugium with a deep sand bed on August 2'nd. That really did nothing to reduce my Nitrate level over the course of a month. I added Chaeto algae and illuminated my refugium on a reverse light cycle on 10/9. On 10/25 the Nitrate level was still at 25 mg/L. Around this time I became concerned that my light output may be too low. The tank looked dim compared to my refugium which was lit with a single 6500K spiral CF fluorescent bulb. Perhaps some of the problems I was experiencing were due to low light levels rather than elevated Nitrate levels. Being on a budget I decided to purchase four 26W 6500K spiral CF bulbs from Lowes along with four clip-0n shop light fixtures with reflectors. So, by going the cheap route I was able to add 104W of daylight illumination for about $30. These were installed at the back of the tank on October 25'th. At the same time I ordered replacement PC bulbs for my hood. The replacement bulbs were installed on 10/29. All the while I continued to measure the Nitrate level as shown in the graph above.

The bulb I'm using is shown below. It is a 26W 6500K Bright Effects bulb purchased from Lowe's. It has the numbers BE26T3/D and E170197 printed on the label.
From Paul's Reef - Apr 15, 2008

The picture below shows the bulb and hood clipped to the front of the tank for easy viewing.
From Paul's Reef - Apr 15, 2008

Here is what the tank looks like with the extra bulbs and clip on fixtures.
From Paul's Reef - Apr 15, 2008

So what does the graph show? It shows that four days after installing the four spiral bulbs at the back of the tank over my live rock my Nitrate level dropped from 25 mg/L to 10 mg/L. At this point I installed the new PC fluorescents. Three days later, on 11/1, the Nitrate level had dropped to 5 mg/L. Up to this point this was the lowest I had ever measured. Five days later the Nitrate level was cut in half again and were reduced to 2.5 mg/L. Another 5 days later the Nitrates dropped to 1 mg/L. The Nitrate levels have continued to drop and are now at 0.2 mg/L.

In all the reading I did about techniques for reducing Nitrate I never came across anybody recommending increasing illumination. I read about using a deep sand bed and using macro algae such as Chaeto. I also read about Nitrate sponges and Nitrate coils. I tried the DSB and Chaeto and did not see a reduction. You can argue that I did not try the Chaeto for a long enough time period. True, it's possible that the Chaeto helped. However, I would have expected to see a gradual decline beginning with the introduction of the Chaeto. However, two weeks after the introduction of the Chaeto the Nitrate level stubbornly remained at 25 mg/L.

The chart, however, suggests that the catalyst for the Nitrate reduction was the addition of the cheap spiral 6500K CF bulbs. After the introduction of these bulbs the Nitrate levels literally fell off a cliff. But why?

It is my belief that the algae that was already in my tank took off after the additional lighting was added. The color of my live rock noticeably changed with the increase in illumination. Looking closely at the rock you can see very fine green algae growing over the coraline. This algae is remaining very short and well kept and provides natural grazing food for my tangs. I do not have any hair algae growing that I can see although I did fear this would happen. At times fine bubbles can now be seen over my rock clinging to the fine algae. I'm not sure of the origin of these bubbles. I do not believe they are microbubbles that are captured by the algae. Perhaps they are nitrogen bubbles generated anaerobically in the live rock and trapped by the algae. Perhaps they are produced by the algae. Is it possible that the algae is reducing the flow of oxygenated water to the rock and encouraging anaerobic denitrifying bacteria to thrive.

From Paul's Reef

This fine algae which has a lot of live rock surface area to grown on may be absorbing the Nitrate. The tangs are keeping the algae manicured. One would think that the Nitrate would be reintroduced in the tangs' waste. Perhaps it is but it is being quickly reabsorbed by the algae to repeat the cycle. Is it possible I have created a self-sustaining ecosystem?

Some might suggest the the reduction of nitrate occurring with the additional lighting is strictly coincidental. Twenty years of engineering experience has taught me that true coincidences are rather rare. Usually, there is some causal relationship between the two observations.

I would encourage others with Nitrate problems to try the simplest approach first. There is nothing simpler and cheaper than adding 6500K spiral bulbs from Lowes or Home Depot to the back of your tank. This is certainly cheaper and faster than building a refugium. Having some shop lights clipped to the back of your tank may not provide you with the best look. Eventually, after you are convinced it works, you can build a nicer hood. If your tank responds as mine did you may have the results you are looking for in about four days.

I'd be interested in knowing your experiences. Please send me an email at