Dosing phosphates to bring down nitrates… please explain!

reefiniteasy

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So I know the Redfield ratio says nitrate to phosphate ratio should be 10:1. I do a 5-gallon water change every other Sunday. Pre-change was 26.1ppm NO3 and .02ppm PO4. Post water change the tank tested 20.7ppm NO3 and .03ppm PO4.

I made a post on Instagram showing my results and my scrubbers growth over the last two weeks. The gentleman from Clearwater Scrubbers commented that I need to dose phosphates to get my nitrates down. Can someone please explain this to me?

If the tank looks great and I’m cleaning the glass less since installing my Drop1.2x scrubber is this something I should be doing? Should I be dosing phosphates.
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Randy Holmes-Farley

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So I know the Redfield ratio says nitrate to phosphate ratio should be 10:1. I do a 5-gallon water change every other Sunday. Pre-change was 26.1ppm NO3 and .02ppm PO4. Post water change the tank tested 20.7ppm NO3 and .03ppm PO4.


That is one of the the biggest myths in reefing.

The actual Redfield ratio never said anything about what levels should be in a reef tank. Redfield himself may never even have heard of a reef tank.

Ignore ratios and any advice to follow them. It is NEVER better to use ratios than to aim both N and P to desirable levels, such as

2-10 ppm nitrate
0.02 to 0.1 ppm phosphate

In this case, I think it unlikely that 0.02 ppm phosphate is limiting organism growth, but it is possible, and thus it is possible, but not guaranteed, that boosting phosphate by dosing it will boost growth and cause increased uptake of N.
 

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So I know the Redfield ratio says nitrate to phosphate ratio should be 10:1. I do a 5-gallon water change every other Sunday. Pre-change was 26.1ppm NO3 and .02ppm PO4. Post water change the tank tested 20.7ppm NO3 and .03ppm PO4.

I made a post on Instagram showing my results and my scrubbers growth over the last two weeks. The gentleman from Clearwater Scrubbers commented that I need to dose phosphates to get my nitrates down. Can someone please explain this to me?

If the tank looks great and I’m cleaning the glass less since installing my Drop1.2x scrubber is this something I should be doing? Should I be dosing phosphates.
40387811-B365-4F71-B016-DD4299FFE925.jpeg
If you want to increase algae growth in the scrubber, you could try dosing PO4 because the actual amount might be lower than than the Checker reads. If you are comfortable experimenting, dose PO4 to 0.05-0.1 ppm and monitor it every day to get a sense for how quickly your system is removing it. You might find it drops rapidly.

Another possible way to increase algae growth is to dose trace elements. This might make a difference if your system is depleted in certain trace elements. Try ChaetoGro and start with ~1/10 the recommended dose. I suggest this level as a starting point based on Ulva growth experiments in my system and the recommended dose making my Mexican turbos sick.

The Redfield ratio is not an important concept for good algae growth. Give algae enough of everything and it will consume the ratio it wants. Think absolute amounts not ratios of amounts.
 

KStatefan

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It seems like that ratio is being talked about a lot more lately for some reason. From 1934 the ratio was 106:16:1 for C:N:p now people talk about 10:1 instead where does that number come from?

Using @Randy Holmes-Farley target numbers from above you will have a ratio between 500:1 and 20:1 or am I calculating the ratio incorrectly
 
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reefiniteasy

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That is one of the the biggest myths in reefing.

The actual Redfield ratio never said anything about what levels should be in a reef tank. Redfield himself may never even have heard of a reef tank.

Ignore ratios and any advice to follow them. It is NEVER better to use ratios than to aim both N and P to desirable levels, such as

2-10 ppm nitrate
0.02 to 0.1 ppm phosphate

In this case, I think it unlikely that 0.02 ppm phosphate is limiting organism growth, but it is possible, and thus it is possible, but not guaranteed, that boosting phosphate by dosing it will boost growth and cause increased uptake of N.

If you want to increase algae growth in the scrubber, you could try dosing PO4 because the actual amount might be lower than than the Checker reads. If you are comfortable experimenting, dose PO4 to 0.05-0.1 ppm and monitor it every day to get a sense for how quickly your system is removing it. You might find it drops rapidly.

Another possible way to increase algae growth is to dose trace elements. This might make a difference if your system is depleted in certain trace elements. Try ChaetoGro and start with ~1/10 the recommended dose. I suggest this level as a starting point based on Ulva growth experiments in my system and the recommended dose making my Mexican turbos sick.

The Redfield ratio is not an important concept for good algae growth. Give algae enough of everything and it will consume the ratio it wants. Think absolute amounts not ratios of amounts.
So I added the scrubber because I was cleaning the glass daily because I always have a ton of film algae and I had three pockets of hair algae in the display (on two corals and one spot on the rocks). I always tested 0.0ppm PO4 with the Hanna Checker. But obviously it was higher.

Now that I have the scrubber running for the last two-ish months I’ve had to clean the glass less and the pockets of hair algae have all but disappeared. I actually cleaned the scrubber yesterday and pulled out a nice wad of hair algae so it is doing what I want.

The thought of dosing PO4 makes me nervous. I’m going to remove the shade screen from inside the scrubber as SM Filtration recommends and I’ll see what kind of growth I get and I’ll go from there.

I might try the trace elements. I know from my last ICP I am low in the following.
Thank you both. I definitely have a lot to think about. I’m sure glad we have this forum, otherwise I’d be listening to random people on IG and have no one to bounce ideas off of.
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reefiniteasy

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I should also mention that I use ClearFXPro in my media caddy. It has a resin that removes PO4. It’s been in for 2 months. I w used it for years. It’s probably about depleted right now. I will be replacing it with the ClearFX Reef which does not remove PO4. Which I think will compliment the use of the algae scrubber.
 
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reefiniteasy

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So I exhausted the ClearFX Pro and replaced it with ClearFX Reef. The reef formula does not have the phosphate removing resin. This did the trick. I tested nitrates and phosphates today, a week after my last water change and PO4 is at .33, an all time high for my tank and nitrates are the best they’ve been at 20.9ppm. I think I found the magic sauce. The scrubber is growing like mad and the display looks phenomenal. Apparently I like it dirty.
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