Algae growth AFTER Carbon Dosing Drops Nutrients

[divetoday]

Hi folks,

I have had extremely low (mostly 0) phosphate in my reef tank for the last 18 months, but have battled nitrates. They were regularly in the 50 - 100 range throughout the first 12 months. I kept the phosphate so low by using BRS phosphate removal media.

I started carbon dosing last summer to address the nitrates, and got up to a dosage of 85ml/day in a 150 gallon plus sump. I thought my nitrates had plateaued over the holidays at 15, but they suddenly dropped to almost immeasurable levels 2 weeks ago.

Suddenly, I have a new algae infestation coating rocks that had been pristine with only coralline algae before. Plus, this new algae is a weird mustard green (see pic).

My questions are:
1) where is this algae getting nutrients if the levels are so low?
2) is the concurrent appearance of the algae and the low nitrates coincidental or related?
3) what should I do about this ugly mustard algae?

Appreciate any thoughts or experience you might have with mustard algae! [emoji41]

 

[mcarroll]

Probably dino's or chrysophytes based on your conditons, but I admit that's a different look than we're used to....even from chrysophytes, which can be "greenish" sometimes.

Is it flat or "goopy" (2D or 3D)?

Is it tough, powdery or slimy?

Can you get a closeup photo?

Even better, can you get a shot of a sample through a microscope? ($10 and up if you don't have one; see: Selecting a microscope)

 

[divetoday]

Definitely flat, will have to look up chrysophytes, but in all respects normal algae except for the color.

 

[mcarroll]

Either run a R2R search for the term or hit this tag: #chrysophytes

(or both!)

 

[mcarroll]

Somehow I completely neglected to mention that your ultra low phosphate level is something that is to be avoided – it will cause corals to be unhappy and strange/harmful algae to grow.

The level of phosphate is probably the reason for the relatively elevated nitrogen levels too.

 

[amazongb]

What are you using to carbon dose?

 

[mcarroll]

I must really be distracted!

Stop carbon dosing immediately.

It's dangerous under the circumstances and chances are you won't end up needing anyway.