Ultra Low Nutrient Levels and Supplements



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Feb 13, 2021
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Chicago, IL
I have been keeping the tank low on major nutrients with Nitrate around 0.5ppm and Phosphate below 0.04 ppm. Everything is thriving including SPS corals and I have had practically zero algae problems, even getting through the ugly stage (lights at 23K help, no doubt). The problem is keeping these levels stable. Last test done this weekend shows both values at zero (which is probably not zero, but too low for the test kit to show. I am using Red Sea on all tests).

I am now starting to see red hair algae growing. It looks a little bit like cotton candy algae but spreading in the same way as green hair algae. I have never seen it before, but thanks to the info on this forum, I will be getting a turbo snail to deal with it. This algae is being reported in low nutrient tanks.

I've been dosing Reef Energy Plus daily until recently and switched to Reef Plus since it's dosed less often and doesn't discolor the water as much. That's the only change I've made. Would trace elements, carbohydrates, amino acids, etc. eventually break down into nitrates and/or phosphates? Could this be fueling the algae growth?

I'd like to continue to keep the nutrient levels low as they more closely replicate natural reef environment, keep corals happy and prevent the red algae problem.

What's the best way to approach this issue?


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Jan 28, 2018
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So you want to raise nutrients slightly but keep them fairly low?

Is the tank new? Is it fully stocked?

Why not add another fish or two to keep things from bottoming out.

Nano sapiens

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Apr 25, 2010
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Northern California
As you are noticing, just like corals not all alga are alike. It's a general misconception that all algae can't grow well in very low nutrient conditions. Many species of 'turf algae', especially, thrive on even the most pristine natural reefs. They are typically not conspicuous, however, since herbivores are constantly 'mowing the lawns' (remove/exclude all herbivores for a few days on a patch of reef and the algae takes off and becomes very conspicuous). So, sufficient herbivory is a main component along with depriving turf algae of settlement space (promoting coralline algae and lots of coral cover). To deal with existing patches, hydrogen peroxide can be used effectively (lots of threads on R2R and other sites on how to use it).

That being said, IME there is value in keep nutrient levels relatively low, but within accept reef keeping norms (for newer systems). Some of the worst pest algae (hair algae, bubble algae, etc.) blooms occur in higher nutrient conditions.

When you add nutrient rich products to a system, they can be directly utilized 'as is', but much of it is also broken-down into simpler forms by the resident microorganisms. All this can happen without much (if any) noticeable effect via test kit readings as long as the input isn't excessive/continuous. So, it's common to see a reef system that one may think is 'nutrient poor' (very low or '0' test kit readings), but in reality the nutrient throughput can be substantial as the nutrients are quickly being utilized by all the various organisms that are present (this is the case in my very mature system that has relatively high and constant nutrient input, but has '0' PO4 and 3-4 ppm NO3).

Do you take notice when your coral starts stretching or shrinking?

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