Dosing Phytoplankton: Is It Good for Your Aquarium?

Dosing phytoplankton can provide many benefits for some aquariums, and yet may cause problems for others.

Determining whether or not it’s a good idea to use it can often be difficult.

And a quick look on popular saltwater aquarium forums reveals quite a raging debate.

Some folks argue phytoplankton is the foundation of the food chain in our oceans, and is therefore beneficial to life in a reef tank.

Others say it can’t be directly consumed by coral or most other aquarium inhabitants … and therefore does nothing except to add unneeded nutrients to the water.

I’ve tried dosing phytoplankton in my 24-gallon mixed reef aquarium on two different occasions. Each spanned one month.

The only change I noticed the first time was an decrease in the time it took for film algae to grow on the glass. Before dosing phytoplankton I had to clean my glass once every 4 days.

After I began dosing phyto, I had to clean it every 3 days.

Bottle of Phytoplankton

There were no changes in coral growth or color. And no other noticeable changes, so I stopped dosing it.

Over-filtration¬† in the months that followed caused my water to become a bit too ‘clean’. I noticed slower growth and paler color in some of my corals. So, instead of running a skimmer and filter floss together, I decided to use just the skimmer.

After a couple of months my nutrients were still measuring in a nice, low acceptable range: 0.01 phosphates and less than 3 ppm of nitrate.

But there was still just enough of an increase in each for my corals to regain their vibrancy and grow a bit quicker. They were consuming the extra nutrients before they could cause my measured values to rise.

Now, you’re probably wondering, “what does this have to do with dosing phytoplankton?”

Well, I also noticed another unexpected surprise. New sponges began to grow on my live rock.

When I first set up my tank, I used live rock from Tampa Bay Saltwater. It was COVERED in barnacles, sponges, and other life.

Unfortunately, as my tank matured, and my nutrient levels came down into proper ranges, they slowly died off and faded away.

When I saw these new sponges starting to appear, I thought dosing phytoplankton might help them to spread even more.

So tried dosing phyto for a second time.

The result?

The same as the first time. I’ve had to clean film algae off my glass twice as often. But I’ve noticed no difference in the growth rate of the sponges or anything else.

So I’ve stopped dosing it. And I doubt I’ll try it again.

It is apparent to me now that my tank does not have enough phytoplankton-dependent life in it any more to make it worthwhile. The nutrients from uneaten fish food, fish poop combined with twice-weekly feeding of coral food is enough to keep my tank happy.

However, I do wish I had known about dosing phytoplankton when I had first set up my tank with that live rock.

All those original barnacles, sponges, porcelain crabs, and the myriad of other filter feeders would probably still be alive and thriving if I had started dosing phyto then.

That is perhaps the biggest key to knowing if it’s worth dosing phytoplankton in your tank.

If you have a lot of filter-feeding critters in your tank, it is definitely worth giving it a try.

On the other hand, if you only have a few, or none, then dosing phyto probably isn’t worth it. You will only be wasting money and adding unnecessary nutrients to your tank.