Why does GFO lower PH?

How much of a decrease do you measure?

Reduced PO4 and localized precipitation of calcium carbonate near the gfo could reduce alk which might effect ph but it shouldn't be by very much unless large quantities of gfo are used.
 
I see a decrease of .10 in my daily range. I use 25% less than what is suggested on the BRS reef calculator.
 
Steve are you sure it is the GFO ? I may be that pulling the PO4 out of the water column increases calcification rates of coral which reduces, Ca++, Alk and at times pH. You would need to monitor the daily demand's of the tank with GFO and w/o GFO
 
I did notice that my alk dropped from 9.3 to 9.0 in one day and didnt put the two together. I will keep an eye on it. I typically only run gfo when I notice a spike in po4.
 
As Boomer notes, PO4 inhibits calcification so reducing it may increase demand for alk and calcium via biotic,ie growth by calcareous organisms and abiotic precipitation of calcium carbonate.Monitoring alk and adjusting dosing to variable consumption is a prudent step when using gfo .

Less PO4 might also lead to less phytoplankton;clearer water may thereby enhance lighting intensity a bit as well which may also enhance growth or in some cases slow it.
BTW, PO4 itself is part of total alkalinity which is what we measure albeit a relatively small portion . (Even at very high PO4 of say 1ppm, PO4 would only make up about 0.5% of total alkalinity while carbonate and bicarbonate makes up about 96.5%).
 
I definitely should have paid more attention in chemistry class. My PO4 was .08 when I decided to run the GFO. I have heard many different opinions what is an acceptable level for PO4. Some have said that .08 is ok and others have said anything over .03 is not good. Thoughts?
 
There is no reliable test kit or meter for us that if it reads 0.03 it is 0.03. This is more or less the lower limit called MDL (Minimum Detection Limit ) of any on them an then you have to throw in what we call noise or accuracy. Meaning, a kit may claim 0.03 MDL but has a +/- 0.03 accuracy, which means it is somewhere between 0.0 - 0.06 ppm. That is like throwing a dart at what it really is.
 
Boomer said:
There is no reliable test kit or meter for us that if it reads 0.03 it is 0.03. This is more or less the lower limit called MDL (Minimum Detection Limit ) of any on them an then you have to throw in what we call noise or accuracy. Meaning, a kit may claim 0.03 MDL but has a +/- 0.03 accuracy, which means it is somewhere between 0.0 - 0.06 ppm. That is like throwing a dart at what it really is.
Click to expand...

Indeed good info. Thanks for posting that Boomer. :p
 
I'm beginning to think good old fashion water changes is the better way to correct an elevated po4 level. I have a lot of macro in my fuge and run reverse lighting on it. I don't think I over feed but I'll try cutting back a little to see what happens.



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SPotter said:
Whenever I run GFO I notice that my ph level will drop. Why does this happen and is it normal?
Click to expand...

Spotter, did you mention your tanks normal range of alkalinity? If it's where it should be, using GFO shouldn't create too big a pH issue, so long as you aren't using too much GFO, and your initial PO4 level wasn't too high. :)

Water changes alone may not be good enough, even with zero PO4 in your newly mixed salt H2O.
 
My alk had been pretty steady at 9.3 and when I tested it last night after 24 hrs of running gfo it had dropped to about 9. The ph range has only dropped by .10 on the low and high ends. My po4 was .08 two days ago and when tested last night it was .006. I calculated that I should use .94 cups of gfo for my system but I only put in .75 cup figuring my calculation for actual water volume was a little off. I'll definitely look at the link you provided and will test ca, alk and po4 tonight. As well as check my TDS meter on my RODI line and change the filters.


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FWIW, I notice no pH change when I add GFO, and I'm not convinced there is any significant effect generally, although perhaps some brands have different surface washes before sale. If you are concerned, maybe rinse it with a little tank water before adding it. :)
 
Randy Holmes-Farley said:
FWIW, I notice no pH change when I add GFO, and I'm not convinced there is any significant effect generally, although perhaps some brands have different surface washes before sale. If you are concerned, maybe rinse it with a little tank water before adding it. :)
Click to expand...

I've been using the brs gfo and rinse with RODI prior to turning it on. I really appreciate everyones help and suggestions. It's people like everyone on here that make this a great hobby!


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:D agreed, good folks here helped me.

I'm wondering if 0.1 change in pH with using GFO should be any concern, actually. Sounds like you're a very responsible reef keeper. :)
 
I still learn something new everyday in this hobby, so, I'm certainly no expert, but I'm curious, when you tested your PH levels, did you conduct your tests at different times of the day? Even though I incorporate a reverse lighting schedule between my D/T and refugium, my PH is still lower in the morning but by the end of my D/T light cycle, my PH is always a little higher. Just a thought.
 
I always do my water tests right around the same time every night and my ph is monitored by a controller so I do see the drop in the am and the peak in the pm.


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