P H problems

[bill miller]

I have a 75 gallon tank which the PH runs 7.8 need some ideals on how to fix this problem. Last water change one week ago 20 gallons coral pro salt used R and O water used magnesium is 1000 calcium 400 Do not know what to do .Tank is 1 year old

[rlcline76]

Magnesium is low. Also, keep in mind that it is winter, so you might have CO2 keeping your pH low, as well. I would doublecheck the magnesium, dose. Watch you calcium and KH, too. Your Ca could be a little higher. If you can, post your KH.

[rjrobert]

Common problem in a begginer / new tank so don't feel bad. It's the tanks way of welcoming you to Reef Chemistry 101.

step 1 - get a bucket of magnesium. Raise your levels to above 1300. ( I keep mine around 1400)
step 2. Check your alk raise it to around 8.2/3.1dkh
I don't think Calcium affects PH but in a reef tank I like a level of 425 but 400 should be just fine.
step 3. test PH two different times during the day. Right before the lights go on and right after they go off. Chances are you will have about a .15 - .20 difference. Let us know what those to values are. I posted a screen shot of my PH from a month ago when I was having a problem with CO2 in the fish room and it was lowering my PH. If you'll notice the graph the PH rises and falls based on the light cycle due to CO2 uptake during photosynthesis. Your PH will vary during the day as well.
step 4. Have patience. It is common for new tanks to having lower PH. A PH of 7.8 is a little low but in my opinion your still in the safe range as long as that is the lowest value in the morning.



Their are several good articles in http://www.advancedaquarist.com and the ReefKeeping magazine on PH and basic reef chemistry. They should help alot.
Let us know if we can help further. And welcome aboard!!

Bob^2

[bertoni]

That pH isn't that bad. What's the alkalinity? I agree that the problem most likely is carbon dioxide.

I agree that the magnesium level is low, but that won't affect the pH.

[rjrobert]

Bertoni, You are the man so just as a point of discussion. Wouldn't a real low Mg would cause a disruption of photosynthesis do the the needs of the cellular algae in the water requireing a normal level of Mg to replicate thus lowering the CO2 uptake capabilities of the tank thus lowering the PH? Not sure if it's significant but wouldn't it be at least one cause.

[bertoni]

Maybe, but I don't think the Mg is low enough to cause such a problem. Also, low pH problems usually are night-time issues, when the algae aren't doing any photosynthesis, anyway. You could ask in the chemistry forum, and some more knowledgeable people might be able to answer the question.