Low pH and Alkalinity

lagnew904

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So I really hate to add threads on issues that have been answered before and are searchable. However I'm not able to find a thread for my exact circumstance.

I've been chasing high nitrates after completing cycle so I've been doing biweekly water changes of 50% to get it down fast and efficiently. Yesterday I performed the third water change and got my nitrates to 5ppm where I'm happy for the time being.

During this I've matched salinity at 1.025 or best I can tell using a refractometer on not the best eyes. (Have a digital one coming this week to eliminate that variable)

I tested 24 hours after last water change and these are my current parameters.


Temp - 78.4
salinity - 1.025. (Refractometer)
pH - 7.6 (red sea)
ammonia - 0 (red sea)
nitrite N02 - 0 (red sea)
nitrate N03 - 5 ppm (red sea)
Alkalinity - 6.7 dkh (Hanna)
Phosphate - 0.03 (Hanna)


Up until this point I've been able to maintain a consistent pH of 8.0 and alkalinity of 7.3 Dkh using the same tropic Marin pro reef. I know this salt is low in alk but it's always matched their spec.

I'm trying to figure out why my pH and Alkalinity dipped so low after the change. Is it possible I'm not mixing my salt correctly? I've been only checking salinity and temp before adding to the tank. Would a small amount of variation in the salinity that I cant see on the refractometer, caused by me putting less salt, result in the lower pH and alk?

Eventually I'm going to dose to raise alk around 8.5 anyway but before that I need to get a handle on the inconsistency at water change.
 

Randy Holmes-Farley

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I don't have a lot of confidence in pH kits (meters are better since you can check them), but if both your alk and pH numbers are correct, it reflects high CO2 in the water, not so much the alkalinity.

Try measuring the alkalinity in the new salt water if you think it may be contributing to lower tank alk.
 
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lagnew904

lagnew904

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I don't have a lot of confidence in pH kits (meters are better since you can check them), but if both your alk and pH numbers are correct, it reflects high CO2 in the water, not so much the alkalinity.

Try measuring the alkalinity in the new salt water if you think it may be contributing to lower tank alk.
Ahh I forgot to mention that. Test was after windows open and new water so I didn't think c02 would accumulate that quickly but you are probably right. I'll try it with the air stone method.

I definitely agree with you on the pH test kits. I wasn't expecting high accuracy but more or less looking for consistency. If it fails low it should fail low the majority of the time correct? I know there is probably more variables than that but I was expecting repeatable results either good or bad.

I've tested pH before on made saltwater as a control and got between 8.0 - 8.2

Any suggestions on a good pH probe? I don't have an Apex yet so that one is on hold.
 

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