How to stabilize fluctuating phosphates in a nano?

ilyad · Feb 28, 2018

Hello all and Randy,

I have a hard time regulating my phosphates and keeping them within an acceptable level. The levels are always either too high or too low. Any help would be greatly appreciated.

First, a little background... the tank is a 18 inch cube nano with a sump. Total water volume is 24 gallons (this takes into account the sand, rock, and sump). The sump unfortunately does not have space for a refugium. I have tried to run the Pax Bellum multiple times with no success - the chaeto just slowly dies out over a few months. That being said, I do have a skimmer and it typically does pull decent skimmate. I also run filter floss in the overflow area (mine is external and I have DIY'ed a tray where I can put the filter floss) and change it out every few days.

I have media reactors but not sure if they would be useful due to the small size of the tank. I used to run both, carbon (changed every 2 weeks with a water change) and GFO (once a month), but that would keep my phosphates almost undetectable using the Hanna ULR tester which would read 0. I have noticed coral lose coloration, which I assumed was due to water being too clean. I then removed the Carbon and GFO, and over several months saw an improvement in the coral. Unfortunately, now the phosphates are drifting up and reading at a level of 0.2 which is 10x the recommended target range. I found an online calculator which told me that if I wanted to use RowaPhos, I would need to use only 2 tablespoons to bring it form 0.2 to 0.02. How do I even begin running so little media in a reactor?

What would you do to battle this situation?

PS. I feed my fish on average 5 times a week, and since Ive removed the carbon and GFO, I increased the frequency of my water changes to 5 gal per week. Yet I still see phosphates slowly drifting up.

PPS. One odd thing I've had with this tank is that even when my phosphate levels were reading 0, my sand always had a slight brownish (dirty) hue. I just cannot get it to be that nice white color. I have not noticed any change in sand color when phosphates were 0 or 0.2 now. Maybe this is something that is useful to know regarding this situation.

Thanks in advance.

Reeferdood · Mar 1, 2018

Have you checked for phosphate in your new water or mix?

Randy Holmes-Farley · Mar 1, 2018

I wouldn't agonize over the phosphate level near your high end (0.2 ppm) if you do not have a bad algae problem, but I think you can use as little GFO as you want (a reactor can have just a tiny bit in it), or larger aluminum oxide binders in a media bag.

Jers_Reef · Feb 15, 2023

Hi ilyad,
Wondering after finding this ole thread in my present query, if you ever got your phos to level out? What’d you learn?

I’m having a similar struggle with my ~1yo 18x18x18 cube (Aquatop AIO 24). When I’m feeding conservatively and doing my regular water changes, Hanna ULR will read around 5-6ppb (0.02ppm), or occasionally zero. So then I worry it’s too low and I feed a little heavier, on different days dose Red Sea AB+, or broadcast/target Oyster Feast, or Reef Roids ~1/8 tsp 2 x/week, and/or lately been trying some small amounts of Reef Frenzy (acans seem to love it!). I’ll hit 50ppb ish (0.15ppm) again fairly quickly, and then back off a few days and then right back down to 5! From what I read, 0.15ppm is at or near upper limit, but not too bad. Nitrate is also ok I think, ~10ppm, which I think is good, right? Ammonia 0.0-0.1 by the color chart, so I don’t think I’m totally over feeding. Right?

Main concern and question is whether the phos fluctuations from 0.02 to 0.15 are going to cause problems by themselves? Bad???

Wondering if too much GFO or just a normal challenge with a nano reef to swing high after feeding and then “low to zero” on a 24-48hr cycle. Obviously I’d like it flat and in some awesome sweet spot, but haven’t cracked the code yet.

After I lost my first digi and accropora to STN last fall (wasn’t totally surprised with the young age of the tank), I started testing more, and feeding the fish and corals more. I added a canister reactor to manage the increased bio-load and control phosphate. The reactor is one of those basic, single chamber, canister units that come in a kit from BRS with a sicci 1.5. The little sicci just barely fits (perfectly fits?!) into my return chamber. I draw from the bottom of chamber to the canister, then dump back into same chamber where stock return pumps back to display. I try to be conscious how much GFO vs carbon I add, only change 50% at a time, and I only use about 1TBS GFO. Carbon change out is about every 2–to-3 weeks, and gfo change out is probably monthly or even 1x per 2 months.

New digis and acro are doing ok, but color could be better. Sorta seem faded. Acans aren’t doing great, but the acan struggle is likely flow too high.. Torches and hammers are happy. Zoas are doing ok, not great. Other random stuff doing ok. alk around 9. salinity 1.025, 77F. Reefi UNO going on it, set to about 110W at noon. Can increase up to 150W if you all think it would help.

thanks for reading and commenting.

Randy Holmes-Farley · Feb 15, 2023

I have not seen any reason to believe that hourly changes in phosphate based on feeding timing is an issue. I don't think it's a good idea to keep changing the nutrient levels frequently by changing the feeding levels frequently.

I'd pick a feeding schedule and stick to it, with slow changes if changes are warranted.

10 ppm nitrate is fine, and I expect phosphate moving from 0.02 to 0.15 ppm over the course of a day is not a concern. That phosphate level is likely better than 0.01 or less.

Jers_Reef · Feb 15, 2023

Randy Holmes-Farley said:
I have not seen any reason to believe that hourly changes in phosphate based on feeding timing is an issue. I don't think it's a good idea to keep changing the nutrient levels frequently by changing the feeding levels frequently.

I'd pick a feeding schedule and stick to it, with slow changes if changes are warranted.

10 ppm nitrate is fine, and I expect phosphate moving from 0.02 to 0.15 ppm over the course of a day is not a concern. That phosphate level is likely better than 0.01 or less.

Thanks for the quick reply and validation! More fun to “feed heavy” anyway, and cool media reactor is squashing the phos like I hoped. Will do wrt committing to the feeding regimen .