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Within the first month of setting up my 75 gallon saltwater tank, I had hair algae. Just a little at first, but then it seems to almost take over the tank within just a few days.

If you aren’t familiar with hair algae, consider yourself blessed. Hair algae is this dark green hair like algae that grows on your sand bed, rocks, filters, power heads, snails, etc. Green hair algae seems to grow on just about anything and I swear if you watch it long enough I think you can even see it growing!

I purchased a clean-up crew from Saltwaterfish.com consisting of various types of algae eating snails, along with a lawnmower blenny. They made a dent in it, but it seemed to come back almost as quickly as the clean-up crew consumed it.

Turns out, green hair algae is a common problem in saltwater aquariums, but not normal. The most common cause is something called phosphate (PO4). Phosphates serve as the primary food for bad algae such as hair algae. Phosphates come from different sources, but primarily unfiltered tap water and common saltwater aquarium products like carbon, sea salt mixes, and various buffers.

My initial hair algae problem was due to using tap water to make up my saltwater mixture. Don’t EVER use tap water in a saltwater aquarium. Dechlorinated or not, tap water contains minerals and chemicals that will negatively impact you water quality. My original hair algae problem was resolved by both beginning to use RO/DI water and by maintaining near perfect water conditions and mineral levels. This is achieved by frequently testing your water, adjusting your various chemical levels with supplements, and by doing frequently water changes. Within a week, my hair algae died and was gone. My tank stayed pristine for weeks. It was gorgeous, beautiful white sand and Coraline covered rocks.

The return of the Hair Algae

Some weeks later, I noticed few small areas of hair algae starting to appear again. I didn’t think much of it as I hear of many very experienced hobbyists having small hair algae blooms here and there. Well, a few weeks later and my tank was again covered with it. All of my live rock and sand is covered with 2-3″ strands of dark green hair algae!! This hair algae was far worse than the last, the stuff was everywhere.

What did I do wrong? Why did it return? At first I didn’t have a clue. But I started aggressively attacking it by:

• Purchasing a Clean-up Crew - I purchased a clean-up crew consisting of snails, hermit grabs, lettuce nudi-branch, and some sea cumbers. I also bought another lawnmower blenny.  Check out Saltwaterfish.com, I’ve had great success with them.
• Doing frequent water changes - I started changing 10-15% of my water weekly, both to reduce phosphate levels and to replenish the tank with necessary nutrients.  I wrote about a how I do water changes a while back.
• Reduced my feeding - I cut back on how much I was feeding, switching to every other day rather than daily. I also payed close attention to not feeding them more than they could eat in 5 minutes.
• I wet skimmed - I lowered the collection cup on my skimmer to begin wet skimming instead of dry skimming. This would remove more nutrients from the water and hopefully pull out any algae spores in the water.
• Filled my canister filter with Phosban - Phosban is a phosphate absorbing product. I filled two micro bags full and placed them in my canister filter to absorb any excess phosphate that might be feeding the algae.
• Purchased a TDS Meter - I also bought a TDS meter to ensure my RO/DI water was pure. The meter showed 3, which isn’t perfect but well under the required 5. TDS meters are inexpensive and will provide a level of confidence on the quality of water you are placing in your tank.
• Manually pulled the algae out - I had read that an effective way to remove hair algae was to physically pluck it out. We did this almost nightly for weeks. It did help, but didn’t solve the problem.

None of these things made a difference, at least not to the algae. I’m sure my water quality overall went way up which made my fish very happy, but the algae continued to grow. Our tank looked gross. The biggest problem was that we were in the process of trying to sell our house, and my aquarium is one of the first things you notice when you walk into the house.

Nitrates

I headed back out on the internet and continued reading about hair algae and the causes. I’m not sure how I missed it, but while Phosphates are on of the main causes of hair algae, high nitrate levels are as well. I continued to read focusing on nitrates and trying to identify the cause of the high nitrate levels. Turns out, canister filters and their filter media can serve as Nitrate beds and cause high levels of Nitrates. I immediately turned off my canister filter.

We continued manually removing the green hair algae and low and behold it stopped coming back. What we couldn’t remove slowly started turning brown and presently there is only a small amount left. It will take some time for the decayed algae to go away and my tank to look pristine again, but I see the light at the end of the tunnel. The canister filter was the problem all along!

Ongoing, I won’t be running my canister filter all the time. I’ll only use it for short periods of time to polish the water, run carbon or other buffering products (like Phosban). Going forward, I’ll rely solely on my protein skimmer and live rock to keep my tank clean and filtered.

I hope I never see hair algae in my tank again!