Chaeto Growing...Phosphates Zero (help!)

[tanknana]

We have struggled getting chaeto growing in our refugium and finally have it doing well. Now, we are struggling to get our phosphates up (they are at 0.0) without constantly dosing Phos Feed (4ml 2x week) and it isn't enough...zero the next day. Everything else has been stable. Is this normal with chaeto and we will be constantly dosing? (180gal over a year old) Other than this, the tank looks great with no algae issues or anything else. Doing weekly water changes (10%). We mostly feed frozen food with a tiny pinch of dry. Dosing chaeto gro and phytoplankton (and of course calcium and alkalinity).
Our parameters are:
Ph 8.1
Alk 8.9
Phos 0.0
Nitrate 4.9
Calcium 420
Any suggestions/insight?

 

[Randy Holmes-Farley]

Three options:

Reduce the light cycle or intensity on the chaeto, which will consume less N and P.

or

Keep it the same and dose N (I do this one to keep my macroalgae exporting P; I dose food grade ammonium bicarbonate)

or

Feed more, keep the chaeto the same, and allow nitrate to rise (which is fine, IMO).

These are my nutrient target suggestions:

Randy’s Thoughts on Nutrient Target Ranges

Thoughts on Nutrient Target Ranges by Randy Holmes-Farley Almost nothing in the world of reef aquarium chemistry causes as much discussion as selecting and maintaining ranges for nitrate and phosphate. Some aquarists want low targets, some want...

www.reef2reef.com

from it:

4. What targets seem reasonable? Of course, that depends on all the other factors at play, such as types of corals, availability of ammonia, particulate foods, etc. However, for a mature mixed reef, this would be how I personally would run it:

• Let nitrate float between 5 ppm and 50 ppm. I’d use gentle export in this range, such as growing macroalgae.
• Above 50 ppm, I’d begin to focus more on reducing it, by organic carbon dosing, turf or macroalgae, etc.
• Below 5 ppm, I’d begin to dose ammonia or feed more. The target level might drop lower if dosing ammonia, just like the heavy in/heavy out scenario where nitrate may not be as needed.
• Let phosphate float between about 0.06 ppm and 0.3 ppm. This range is higher than I’ve recommended in the past. I’d use gentle export in this range, such as growing macroalgae.
• Above about 0.3 ppm, I’d begin to focus more on reducing it, by turf or macroalgae, or a binder such as GFO or lanthanum (has its own risks to tangs). If a binder: GO SLOW. Turf and macroalgae will typically be slow enough.
• Below 0.06 ppm, I’d begin to dose sodium phosphate or feed more to get the level up.

 

[tanknana]

Thank you so much! You are always a wealth of knowledge that I know I can trust. :)

 

[mcarroll]

Our parameters are:
Ph 8.1
Alk 8.9
Phos 0.0
Nitrate 4.9
Calcium 420
Any suggestions/insight?

... with numbers like that, it doesn't appear that your tank really needs an algae farm growing on it. The algae will definitely be competing with your corals for nutrients. (somebody is being deprived of phosphorus as we speak.)

But if growing algae is one of the goals for your system, then you will definitely have to dose for it just like it was a plant – that means a nitrogen source, phosphorus source and the whole rest too. (seachem and others make full spectrum plant "foods".)

If you're withholding food, certainly get your feeding up to where you want it to be.

But if you're already feeding how you want to then I can't see any reason to keep the keto farm going. At least don't overfeed trying to get nutrients to the algae… Dose nutrients like the algae was a house plant or a hydroponic system. I.e. it's a "pet" and not part of the cleanup crew.