Trying to understand PH

[Neoz]

I have a 18" rimless cube that has been running for awhile now. It has a glass cover that sits on the top of the cube. When I remove the cover and let the top of the tank breathe so to speak my Ph is around 7.9. With the cover on tank the Ph runs consistently at 8.2.

Is it better for the Ph to be at 8.2 or is the difference not worth concerning myself over. If the higher Ph is better then I guess I should always keep the tank covered with the glass? I should also note these readings are during the late afternoon early evenings. Not sure what they are in the am.

Thanks for any help..

 

[Conesus_Kid]

How are you measuring pH?

pH is directly related to the amount of carbon dioxide dissolved in the water. pH will fluctuate from day to day, as well as during a 24-hour cycle due to photosynthetic organisms utilizing the CO2 that's dissolved in the water. The amount of CO2 in the ambient air can also have a dramatic impact on an aquarium's pH. Believe it or not, having a lot of people in the room (with their associated exhalations) can significantly depress the pH.

Check out this chart of my classroom aquarium' pH for the past couple weeks. Notice that it spikes at the end of the day shortly after the lights go out (no more photosynthesis at night). Also, you can see that it peaks higher on Saturdays and Sundays (no mouth-breathers in there all day!).

How many times have you checked pH with the top off vs. top on? Did you have visitors the day it was 7.9? From my understanding, you'd be better off with the glass tops off to better facilitate gas (especially oxygen) exchange with the air.

 

[Namyar]

There is a nice article in Reef Keeping "The “How To” Guide to Reef Aquarium Chemistry for Beginners, Part 3: pH "

 

[Neoz]

Thanks for the information. I'm using the Digital Aquatics PH probe hooked to my Reef Keeper. The top stays on during the day until I get home. Actually the top is off from 3:00pm till 11:00pm. I check the Ph everyday at 3:00pm and there is nobody in the room all day.

I'll do some more reading and see whats up... Thanks..

 

[pascal32]

take a read through TMZs thread on soda lime, lots of good info there:

http://www.reefcentral.com/forums/showthread.php?t=1889552

 

[Gary Majchrzak]

The top stays on during the day until I get home. Actually the top is off from 3:00pm till 11:00pm. I check the Ph everyday at 3:00pm and there is nobody in the room all day.

make sure you're not comparing apples to oranges.

In other words, test pH at 3PM one day after top was on all morning and another day where the top was off all morning (with nobody home on both days!)

As soon as you (or anybody else) gets home CO2 starts to affect aquarium pH. As Scott has shown the drop in pH can be dramatic!

 

[tmz]

As Gary notes , it will vary diurinaly ;more so if you have many photosynthetic organisms in the tank. Sounds like you do. Measure ph at lights out and just before the light come on to get a better sense of it.
In a tank with many photosyntetic organisms during lights on ,the aglae /corals are depleting the CO2 to a level lower than the room air and you get a nice 8.2ph . Gas exchange increases with the cover off and the ph drops to 7.9 as CO2 equilibrates with the room air .
The opposite would occur at night(lights out) when the tank CO2 will increase absent photosynthesis as organisms respire CO2 instead of consuming it and ph will drop. The CO2 may even drop below the room air content and limited gas exchange with a covered tank will likely keep more CO2 in the water and result in lower ph with the cover on.
So, the scenario to encourage higher ph for a tank with relatively high photosynthesic activity would be to keep the glass on during lights on and off during lights out.Obviously a chore most of us would not choose to do.Who nknows someone may make a device to do just that and make money with it.

As long as your ph stays at 7.8 or higher day and night , I wouldn't worry about it . I do, however, prefer to aim for nsw values 8.2/8.3. If you can add some omacroalgae , like chaetomorpha in a lighted refugium to run on an opposite photoperiod it would offset nightime CO2 increases to a degree.

 

[Neoz]

Thanks for the responses. I'm going to run some more tests and posts my results.. Not going to lie up till now I never even concerned myself with ph. Bad idea...

 

[Gary Majchrzak]

concern regarding pH isn't a bad idea but (as Tom noted) as long as pH is 7.8 you're golden. It doesn't sound like your pH was ever dipping that low.....

 

[tmz]

Many get overly concerned with ph magic numbers and use buffers to get to it. Bad mistake since chasing ph with buffers gives a only short term boost to ph as CO2 from the air knocks it back down. Buffers raise the alkainity causing problems with this important parameter .
Steady alkalinity is more critical than ph as long as it is over 7.7 , so dumping in buffers to raise ph is a self defeating activity. I know you are not doing that at this point but if you are thinking about it take it off your list.
Really 7.7 is a red line low in my mind and 8.5 on the other end. If you get to where you wan't to raise it , you have to lower CO2 in the water via gas exhchange( bubbly skimmer, outside air, ripple at the surface) or feed CO2 depleted air to the system via a Co2 scrubber.

 

[Neoz]

Thanks again guys... I've been tracking some numbers. I left my cover on all day yesterday and last night. Just looked at the PH and I'm sitting at 7.6. That is the lowest that I have ever noticed. The cover will be coming today and see if that raises Ph.

I took your suggestion Tom and have moved my Tunes lower in the tank and aimed it up at the surface. I now have a nice ripple effect at the surface. Not too much as this is a rimless tank. Curious too see if this raises the PH as well. I also won't be using buffers. Trying to make this tank very stable and "clean".

I'm trying to learn more about the chemistry side of reef keeping. Before I would test every 12 days and adjust the parameters as needed. I would like to get this more stable. So I'm testing my tank every 3 days to figure out what my usage is for All, Calc, Mag. and make smaller adjustments so I see less swings in those parameters until Santa brings me some dosing pumps...

Must be doing something good. I have never had the coral colors that I'm getting now. My SPS is really colored up good!

 

[tmz]

Good . happy to hear your stock is doing well. I'm conserned about that 7.6 though, Are you sure your measure is accurate?

 

[Neoz]

I'm going to check the probe again tomorrow and recalibrate if necessary. But I removed the cover this morning around 10:00am and the Ph is sitting at 8.12 right now. Been checking it a few times thru the day and noticed it increased all day with the glass cover off. Sat between 8.0 and 8.1 all afternoon and evening.

I'll be leaving the glass cover off tonight and check the reading in the morning. I'll post my results then. That was the first time I noticed it that low. As you said I don't want to get caught up in the number game for PH. But I would like to see it a little more stable and less of a swing. Is there anything I can do different other then leaving the top off all time?

I would leave the cover off all the time but have a few concerns. One is my Reefbrite light sits on the glass top for Actincs. No way to really mount it to my MH fixture. Second is when I get a few fish I won't want any jumpers. The third being the evaporation rate is much higher with the cover off.

 

[Gravesj1s]

Might want to consider limewater it would help with alot of this.

 

[tmz]

Don't know how much room you have but a chaeto fuge on opposite photo period can help swings. A CO2 scrubber hooked to a skimmer air intake tube can raise the ph. Outside air can raise ph if house CO2 is high. Open aerated( ie water movement and suface agitation) in the sump helps too assuming the house air is lower in CO2 than the tank water..

Swings are not a big concern if the ph stays at 7.8 or above. Some natural reef's swing as much as 8.0 to 8.6 at times.
Having said that more O2/less Co2 at night is a good thing to help offset nightime localized low O2 conditions(hypoxia).

 

[Neoz]

Being its a Solana cube, I don't use a sump. Just the stock area in the rear of the tank. I do plan on adding some chaeto and a light very soon. Just waiting on the light. Hopefully sometime next week.

Just read the PH and with the cover off all night it reads 8.0 which is good. As you said not overly concerned as long as it doesn't drop too low. Hopefully cheato will help that.