Why consistently high nitrates and low phosphates?

[FishguyJosh]

I could really use some insight on why my nitrates are consistently around 20 PPM while my phosphates stay low between 0.05-0.08 ppm. I do weekly 10% water changes, have a biopellet reactor, and refugium section (although my chaeto won't stay alive even with a good kessil fuge light). I do have a small bag of chemi-pure in the sump. I doubt it's overfeeding because why would my phosphates stay so low? Any insights appreciated.

Water parameters:
SG 1.025
Alk 8
Ca 450
Mg 1280
NO3: 18-20
PO4: 0.05-0.08

 

[TX_REEF]

that phosphate level seems fine I think, not "too low". That nitrate level isn't overly concerning. Is anything wrong with your livestock that's causing you to be concerned? Do you have a photo of your fuge setup if you're concerned about the chaeto staying alive?

 

[FishguyJosh]

Thanks yeah I'm happy with the phosphate levels. Here's a few pictures of my sump and chaeto area (sump is part of a red sea reefer 425xl). The Chaeto shown is only 1/3 of what I started with a few months ago as it has been slowly dying. I do have a good quality kessil H80 refugium light that I run around 50% intensity for 8 hrs per day.

 

[TX_REEF]

Perhaps try turning up the intensity and/or duration of the light? From some brief research I've read that 100% intensity on the "growth" setting is best, I actually purchased a kessil h80 myself for a new build.

 

[exnisstech]

I just run grow light bulbs in clamp on work light fixtures and chaeto grows well in 3 fuges. I run a 12 hour cycles reverse from DT lights. To be honest I would crank that kessil all the way up. In my exierience you can't give chaeto too much light.

EDIT :One of the fuges with the cheap grow light

 

[jda]

Normally I would say that water changes are enough for your chaeto go grow well. This does not appear to be the case, you might want to dose some iron - you can buy supplements, but Dr. RHF has a recipe using drug store iron tablets that are cheap and pure. I change water, but I also have to dose iron for my chaeto to grow well. Chaeto does not take much light, but lowering that puck down closer to the algae might be OK too.

 

[blecki]

Your ratio of phosphate to nitrate is way off. Anyway the fact that there's any phosphate at all means something else is limiting the chaeto and jda is probably right about the iron. What I think is going to happen is you'll dose iron, and the chaeto will come back and phosphate will bottom out, leaving nitrate mostly untouched.

 

[jda]

I have never found that chaeto can bottom out po4. It can get low, but never to the bottom. Besides, even if the po4 got pretty low, there are other way to get phosphorous to the corals than just having po4. I run a large fuge and skim a lot and my po4 always has 1-5 ppb left, which is plenty.

 

[blecki]

Maybe depends on the sensitivity of the test kit. I would call your 1ppb 'bottomed out' even if it's not literally 0 - what test are you using that has that kind of sensitivity?

 

[jda]

Hannah Ultra Low shows 0 on newly mixed saltwater... constantly. Shows between 1 and 5 on my tank. Easy peasy...

Again, even if I had 0 ppb of po4, how would that mean that anything in my tank is limited for phosphorous?

 

[blecki]

It wouldn't; but if the chaeto had plenty of everything it needed despite reading zero, it would be growing.

FYI the error range on the hanna phosphorus checker is +/- 5ppb. So at that low an amount it's basically a 'zero or not' test. You could have anywhere from a fraction of a ppb to 10ppb.

 

[jda]

The chaeto can also get phosphorous from other sources than po4. My chaeto grows like crazy - have to harvest 5g bucket every few weeks. po4 is fools gold the way that most people use it. The only real value that it has for me is if it starts to get high which means that I need to export more. po4 level is not a sign that there is not phosphorous in the system.

Just because a test has a margin for error, does not mean that it is inaccurate. Since it can tell the difference between fresh salt mix and low tank values, it is doing it's job.

 

[blecki]

Mate I think we're agreeing while talking past each other.