8.02 pH in morning and 8.56 pH at night

[islandkoa]

Does anyone else have extreme pH ranges dependent on time of day? I am considering dosing my tank at around 11ish (at night) as the pH starts to drop, concluding at around 10ish in the morning as it starts to rise again. I'm worried that the upper value would go above 8.56 though. Does anyone have any suggestions on what to do regarding the wide range in pH readings?

 

[bang guy]

It's not uncommon. What are your Alkalinity, Calcium, Magnesium, and Salinity levels?

 

[islandkoa]

Ca is 480-500. Salinity is 1.024-25. Haven't tested Alkalinity in a whilesince it was consistent with pH readings. Haven't checked Mg in a while. Does it effect pH?

 

[bang guy]

Quote:
I am considering dosing my tank at around 11ish (at night) as the pH starts to drop

I'm concerned by this statement. You are dosing something, I am assuming Alkalinity, but you don't know what your Alkalinity level is.

What might be happening is you are overdosing Alkalinity. This will temporarily raise PH and then PH will drop as the Carbonate reacts with your high Calcium. It can be a cycle that gets slightly worse each time it is repeated.

I mention Magnesium because if you are precipitating Calcium carbonate then some Magnesium will be consumed. The lower Magnesium is the more likely your Carbonate (Alkalinity) will react with calcium.

 

[islandkoa]

I only dose (drip line) with alkalinity occasionally when alkalinity readings are low, probably monthly. I'm using purpleup or just Ca mostly to sustain Ca levels. I plan on dosing a ml or two at night when I get my two dosing pumps. I measure my alkalinity every couple of weeks and it seems to correlate with my pH readings which is monitored in real time with my reefkeeper as well as verified on occasion with api test kit. I'm just sort of concerned about the effect my nightly dosing (when readings are low) will have on my pH/alkalinity readings during the day. I'll check my Mg to look for a correlation. I have to read up on this because I didn't know that Mg would be a factor. Thanks

 

[bang guy]

Yes, Magnesium has an indirect effect on Alkalinity. It discourages the Carbonate from reacting with Calcium. Most of your Alkalinity should be in the form of Carbonate or Bicarbonate.

I'd really be interested in what your Alkalinity is.

The PH shift isn't a big concern. It probably has more to do with algae consuming CO2 than anything else but your dosing schedule does not seem very balanced and that could definitely contribute to the PH swings.

Is there a reason you want to keep your Ca so high?

 

[islandkoa]

I kept Ca at around 450 to 480 based on my API test kit recommendations. I just ran a full range of tests this morning 0930-1000. Ca is 500 per API and Red Sea (titration). pH is 8.0 per API and reefkeeper probe. Mg is 1600 and KH is 11.2 both per Red Sea. My lights just turned on. I'll test again tonight to see if there is a difference. I added purpleup and Kent essential elements last night which probably led to my high Mg and Ca. I'll cut back on the Ca to around 450.

 

[bang guy]

How often do you dose Alkalinity? That's a good level, I'm just confused as to why Ca would drop daily and not ALK.

 

[islandkoa]

I dose the alkalinity about once every couple of weeks. Ca, about twice a week. I've just read some informative water chemistry articles in another forum, leading me to believe that factors such as my high Mg (and other trace elements) and CO2 levels are influencing the rate of Carbonate conversion and precipitation. Pretty interesting stuff which would have made good practical material in my chemistry class back in the day. Anywho, this is something which requires tests result plotting to see if there is a correlation with those other factors. I really have to run these tests at night to see the fluctuation because the change in light is the only controllable factor in my aquarium. Hopefully, my alkalinity doesn't rise as much as my pH. I'll see

 

[bang guy]

Alkalinity will only rise with dosing, it's not light related. Do you know how low you let Alkalinity get before you administer another dose?

Do you have a lot of corals or clams?