pH always low!

[VaderWS6]

I just don't understand why my pH fluctuates so much. During the day it reaches about 8.0-8.2, and at night it is anywhere from 7.4 to 7.7.... I add a kalk slurry (half teaspoon) at night which raises the pH to 8.0, but when I get up in the morning the pH is back at 7.4 - 7.7. Will a calcium reactor keep the pH up, or would I still have to add kalk to keep the pH up? Calcium level is 500 and Alk is 10.

[CapitalO]

The low pH is caused by a buildup of carbon dioxide in your water which has an acidic effect (carbonic acid). When the photosythesis in your tank cuts off during lights out, carbon dioxide is being produced from aerobic respiration and drops the pH.

The way a lot of people combat this is running a refugium with reverse light cycle (lights on during main tank lights off). The algae in your fuge will use up the carbon dioxide and prevent such a large drop in pH. Alternatively, a constant (but slow) addition of kalkwasser throughout the night will help resist the pH drop during lights out.

[VaderWS6]

<a href=showthread.php?s=&postid=10991489#post10991489 target=_blank>Originally posted</a> by CapitalO
The low pH is caused by a buildup of carbon dioxide in your water which has an acidic effect (carbonic acid). When the photosythesis in your tank cuts off during lights out, carbon dioxide is being produced from aerobic respiration and drops the pH.

The way a lot of people combat this is running a refugium with reverse light cycle (lights on during main tank lights off). The algae in your fuge will use up the carbon dioxide and prevent such a large drop in pH. Alternatively, a constant (but slow) addition of kalkwasser throughout the night will help resist the pH drop during lights out.

Thats the thing, I do run the fuge lights at night, and its full of chaeto... The air line to my Berlin skimmer draws air in from out doors, and the skimmer runs 24/7 so I doubt its carbon dioxide. I was thinking it could possibly be my sandbed, but its very clean. It just seems that 8.0 to 7.4 is a HUGE drop, especially when it happens within 7 hours... I wonder if my Salifert pH test kit is reading correctly, or maybe it is giving false readings like my older Alk test kit? I need to fix my electronic pH probe..

[CapitalO]

Hmm... other things you could do would be: increase the corbonate alkalinity, increase the aeration in your tank (possibly by increasing flow in display at night) and checking your boron level. Also, if your running a calcium reactor, cut it off at night.

I'm pretty sure if its a day-night pH swing, its CO2 levels. I don't know what else it could be.

[Aquarist007]

try running the fuge light 24/7 and increase the flow through it--made a big difference in co2 levels in my tank.
What's in your tank that would be a high consumer of co2(photosynthesis) and what is your present lighting situation--as in when did you last change the bulbs?

[VaderWS6]

Its a 75 gallon tank, I have crazy flow throughout the tank. 4 1600gph maxi mods, 2 250watt 10k metal halides powered by a PFO HQI ballast with 4 110watt VHO actinics. I have pretty wild surface circulation too, creates waves and whirlpools.

[Aquarist007]

<a href=showthread.php?s=&postid=10991755#post10991755 target=_blank>Originally posted</a> by VaderWS6
Its a 75 gallon tank, I have crazy flow throughout the tank. 4 1600gph maxi mods, 2 250watt 10k metal halides powered by a PFO HQI ballast with 4 110watt VHO actinics. I have pretty wild surface circulation too, creates waves and whirlpools.

ok--shock and awe:)---i'm envious--seriously :smokin: but when were the bulbs last changed
and what co2 consumers do you have in there.

[David Grigor]

Your refugium is likely not sized large enough for your show tank to be able to compensate for the CO2 levels.

Regardless it is a CO2 issue. Dosing kalkwasser evenly throughout the night is likely your best option or increase your refugium size.

CA reactor will only make matters worse.

In most cases, at morning low of 7.7 isn't that bad as long as your ALK is at or above NSW levels.

[CapitalO]

Is the high flow continued through the night or only during the day?

Also, is your test kit measuring total alkalinity or corbonate alkalinity? Your carbonate could be too low; dosing kalkwasser will not replace this either. Only through water changes or dosing.

[CapitalO]

Actually, I'm totally wrong about that last statement. The hydroxide in kalkwasser will interact with dissolved CO2 and form carbonate and bicarbonate... sorry about that

[bertoni]

I don't trust the 7.4 pH reading. Personally, I use a pH meter, so I can't comment on the test kits much. The Salifert seemed reasonable to me when I did some double-checking, but any test kit can go bad. My first step would be to get a second opinion.

A kalk slurry is likely not as effective as a drip, in my opinion.

[VaderWS6]

<a href=showthread.php?s=&postid=10991868#post10991868 target=_blank>Originally posted</a> by capn_hylinur
ok--shock and awe:)---i'm envious--seriously :smokin: but when were the bulbs last changed
and what co2 consumers do you have in there.

Its time for a bulb change next month, but the pH continues the same highs and lows even when the bulbs are new.

[VaderWS6]

<a href=showthread.php?s=&postid=10992179#post10992179 target=_blank>Originally posted</a> by CapitalO
Is the high flow continued through the night or only during the day?

Also, is your test kit measuring total alkalinity or corbonate alkalinity? Your carbonate could be too low; dosing kalkwasser will not replace this either. Only through water changes or dosing.

The high flow is pretty much 24/7, but my wavemaker shuts one of the pumps off at midnight until 7am. I could definitely use a larger refugium (mine is less than 10 gallons). I'll try dripping the kalk. Instead of mixing kalk and letting it settle, can I just mix up kalk in the dripper bucket and let it drip? Wouldn't that be the same as adding slurry, but just sustained throughout the night?

[bertoni]

The problem with not letting it settle is that the drip line might become plugged, but you could try it.

[CapitalO]

I think dripping the kalk throughout the night will help quite a bit. The hydroxide in the kalk will react with the dissolved CO2 in the water to form bicarbonate; so essentially, your removing the pH dropping effect that CO2 creates. I think by dripping it, it would give the hydroxide a better chance to react with CO2, as opposed to sudden concentration of hydroxide that would probably start reacting with other stuff before the CO2.

As for the slurry thing: I always avoid putting any undissolved kalk mix in my tank; I would imagine it would cause a lot of other things to precipitate out of your water that you wouldn't want to.