Is a large Phosphate swing every week ok?

[fryman]

I see others report phosphate as a single number, i.e.: ”My phosphate is 0.08ppm”. Are other reefers’ phosphate readings really that stable or precise?

In my experience, phosphate readings vary quite a lot. My measured phosphate range in the main display over the past month was 0.04 to 0.18ppm, and this is typical. Is that ok/normal?

I believe there is a weekly “cycle”. Just before doing a water change my phosphate is at the highest, about 0.15 to 0.18ppm. But a couple days after I do my weekly maintenance (includes swapping out the GFO), it will drop down to ~0.01 to 0.05ppm. Then it slowly rises, and by end of the week I’m getting 0.15 to 0.18ppm again.

I adjust amount of GFO based on where the measurement is. So, if my reading is low, I add 1/3cup GFO to the reactor (mixed with activated carbon). If it’s high, I might use 2/3 to just under 1 cup of GFO to the reactor. I’ve learned to avoid adding 1cup or more, since this will strip phosphate below detection. But if I don’t add any GFO, my phosphate will skyrocket by end of the week to over 0.6ppm, or out of range for my hanna 736. Of note, I haven’t noticed any effects from high phosphate readings, but I’ve read this leads to brittle coral growth (if chronic). I have upset, and occasionally even killed coral in the past stripping phosphate too fast (or maybe for too long?), using too much GFO. So, I’m using less GFO than recommended on the carton. The trade-off seems to be that it doesn’t last very long.

The hanna has measurement variability for sure, so that’s part of it but if I do multiple successive measurements in a row the range is not nearly as much. I think the reason is because I feed a lot, and GFO is gradually saturated over the week. I use generic (cheapo) GFO from Amazon, but it seems to do the trick. I’ve seen others who feed a lot so I’m just wondering if this much of a phosphate swing is atypical or not.

I don’t have algae issues, or other nutrient-related problems, really. I was just wondering. My display is ~100 gallons plus maybe ~20 gallons in the sump.

 

[Garf]

I see others report phosphate as a single number, i.e.: ”My phosphate is 0.08ppm”. Are other reefers’ phosphate readings really that stable or precise?

In my experience, phosphate readings vary quite a lot. My measured phosphate range in the main display over the past month was 0.04 to 0.18ppm, and this is typical. Is that ok/normal?

I believe there is a weekly “cycle”. Just before doing a water change my phosphate is at the highest, about 0.15 to 0.18ppm. But a couple days after I do my weekly maintenance (includes swapping out the GFO), it will drop down to ~0.01 to 0.05ppm. Then it slowly rises, and by end of the week I’m getting 0.15 to 0.18ppm again.

I adjust amount of GFO based on where the measurement is. So, if my reading is low, I add 1/3cup GFO to the reactor (mixed with activated carbon). If it’s high, I might use 2/3 to just under 1 cup of GFO to the reactor. I’ve learned to avoid adding 1cup or more, since this will strip phosphate below detection. But if I don’t add any GFO, my phosphate will skyrocket by end of the week to over 0.6ppm, or out of range for my hanna 736. Of note, I haven’t noticed any effects from high phosphate readings, but I’ve read this leads to brittle coral growth (if chronic). I have upset, and occasionally even killed coral in the past stripping phosphate too fast (or maybe for too long?), using too much GFO. So, I’m using less GFO than recommended on the carton. The trade-off seems to be that it doesn’t last very long.

The hanna has measurement variability for sure, so that’s part of it but if I do multiple successive measurements in a row the range is not nearly as much. I think the reason is because I feed a lot, and GFO is gradually saturated over the week. I use generic (cheapo) GFO from Amazon, but it seems to do the trick. I’ve seen others who feed a lot so I’m just wondering if this much of a phosphate swing is atypical or not.

I don’t have algae issues, or other nutrient-related problems, really. I was just wondering. My display is ~100 gallons plus maybe ~20 gallons in the sump.

0.01 seems a little low. I've stopped testing for phos to be honest, just never seemed to make any noticable difference if it was 0.1ppm or 1.4ppm.

 

[Randy Holmes-Farley Verified Community Expert]

I don’t know what the implications of a weekly swing are, but that range does not seem large enough to me to be likely to be stressful.

 

[fryman]

0.01 seems a little low. I've stopped testing for phos to be honest, just never seemed to make any noticable difference if it was 0.1ppm or 1.4ppm.

My livestock really doesn't seem to care either if phosphate rises, even quite alot. This happens on occasion, when I get lazy and miss a week (or two). But I know stony coral gets brittle if phosphate is high. I think it's up to you to decide if that matters.

My priority for managing phosphate is not to flat-line @ zero for any "significant" amount of time (more than a day or two at the most). Rarely, I do still get a zero reading but then I'll feed more TDO and check a couple days later to make sure it rises. If I hit zero for a significant period of time I've seen very bad reactions from coral. I don't know how long exactly so to be safe I avoid seeing "0" on the hanna at all.

I'm not perfect with the maintenance but try to keep it under control. The sweet spot for this tank right now seems to be 1/3 to 2/3 cups of GFO in a reactor replaced weekly. It used to need more GFO, so I think when my coral grows out it will change.