DETAILED GUIDE TO PH AND ITS IMPACT ON YOUR REEF TANK
pH as an important measurement for reef aquaria that has complicated interactions with other important building blocks like the availability and saturation of carbonate and bicarbonate in the water. A 0.3 drop of pH is associated with roughly a two-fold drop in carbonate concentrations. A full pH unit would correspond to an approximate ten-fold increase/decrease in carbonate concentrations. As the pH of your aquarium fluctuates up and down with the diurnal cycle of photosynthesis (up during the day, down at night), so to does the available carbonate in your system. It is for this reason that it is best to stabilize this measurement as best as possible. For example, what is the point of stabilizing alkalinity if you are going to let your pH swing 0.3 pts per day?
That said from our experience and based on feedback of others, stability of pH seems more important than an actual number. Although it has been proven that higher pH yields faster growth rates to a point, this is not necessarily the requirement for a successful reef tank. As such hobbyists should seek to minimize swings rather than aiming for a specific high number which can often be difficult to achieve.Quick Index
STRATEGIES FOR CONTROLLING PH
Carbon Dioxide is influential in regulating the pH in water. Measuring the amount of CO2 in a solution is one way to determine its pH. The more CO2 in the water, the lower the pH will be. This effect happens because when CO2 is dissolved in water, a part of it reacts to form carbonic acid. Acids reduce pH. If water is perfectly aerated (this is impossible to achieve) then the water would be considered at equilibrium with the outside air and you would have normal seawater pH concentrations of 8.2 rather steadily as all of the CO2 will be degassed that is of course unless you are indoors and in the presence of living, breathing humans which tend to increase co2 concentrations around the reef tank. Since perfect aeration is nearly impossible to achieve, we will talk about all the forces that can drive pH inside your tank.
PHOTOSYNTHESIS
Photosynthesis drives increased pH during the main photo period by converting CO2 in the water into Oxygen. The effects can be great, and greater still if your aquarium is experiencing a nasty Algae bloom. This is not desirable, as these dramatic rises in pH lead to big swings at night. Rather, it is best to fight back the algae by any means necessary and we're looking for more a + 0.1 increase in the day or less and for that increase to primarily be driven by coralline and coral growth, rather than algae growth.
We can take advantage of the pH increasing effects of photosynthesis at night to offset the diurnal swing by growing macro algae in our refugium on a reverse light schedule from the main photo period. You can also grow algae with Algae Scrubbers if you prefer (we do!).
SKIMMERS
Skimmer's act as an EXCELLENT de-gasser for CO2 in your Reef Tank. Just running a skimmer, any skimmer will improve oxygenation of your water and reduce the CO2 Concentrations. If you don't have a skimmer on your system, you should consider implementing one for this reason alone, never mind the positive effects on nutrient control. Skimmer's can further enhance the pH of your aquarium if you are able to run outside air into their air intake. Many hobbyists have successfully done this and receive a boost of at least 0.1 pH (which is big!). Another strategy that we don't like very much is using carbon dioxide absorbing, color changing media in a reactor. This will allow the skimmer to continue to take in air from your home but without the added CO2 present. The main problem with this is in the cost and maintenance. You will go through tons of CO2 absorbing media and will have to change it pretty often if you want it to remain affective.
ACIDS AND MEDICATIONS
Acid's like organic carbon sources (vinegar) and sulfur can reduce your aquariums pH the same way that CO2 does. Sulfur can often be produced in low oxygen environments such as with the use of a trickle filter or even in a carbon reactor that has clogged up and slowed to a trickle. You may also notice nasty smells of rotten eggs (sulfur) if your skimmer has been off and sitting stagnant for some period of time greater than 12 hours. When you turn it back on, you will send a rush of sulfuric acid into your tank which will impact the pH in the short term. This often resolves itself quickly but you would be wise to be aware. For skimmer's that contain separate venturi pumps consider only turning off the venturi pump instead of the feed pump. This will keep the water circulating even though the skimmer produces no foam and will prevent the anaerobic conditions that lead to sulfuric acid production.
Organic carbon like vinegar and NOPOX is often dosed by hobbyists to control nutrients like nitrates. These acids and other medications can cause a decrease in system pH. For this reason, we tend to only dose organic carbon during the day, rather than at night and we tend to keep our Carbon Denitrators running at a steady, continuous stream rather than a few drops per second trickle (which could lead to the production of sulfuric acid and a reduction of the aquariums pH).
We also maintain our carbon reactors often. If a media reactor is left off for a period of time then they can also produce sulfuric acid in a the low oxygen environment and so if you are turning on a reactor that has been offline for a period of time it is best to discharge the first gallon into a separate receptacle rather than directly into your tank.
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OUTSIDE AIR
One easy solution that hobbyists often implement is to inject air from outside into their skimmer's air intake. Air in our home (and indeed our businesses) can become higher in CO2 due to human respiration. We see these effects dramatically at our coral farm when the buildings are full of living, breathing humans MON-FRI and scarce on Saturday and Sunday. We call it the "weekend bump" and it is solid proof of the dramatic affect our presence in the home can have on our tank.
Want to increase your pH? Try opening the window, it's probably good for you too=P
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BASES (Baking Soda, Limewater)
Bases like Baked Baking Soda (Soda Ash) and concentrated Limewater can have a great affect on increasing your pH. Two part dosing (Soda Ash) is less helpful than concentrated Limewater which has a superior pH benefit. We use both of these supplement our Alkalinity and Calcium anyways so it's a no brainer to dose these at night during the diurnal downward swing of pH. We avoid dosing these during the day so that we can dose the maximum amount at night.
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OTHER NOTES REGARDING PH
At Reef Chasers we aim to maintain our pH at around 8.2 natural sea water level over nighttime hours with a daytime peak of 8.3 this is a total swing of 0.1 or less. We don't always achieve this sort of "ideal stability" but many times we do. For whatever reason, we find that rainy days tend to lead to reduced pH. We can't find any basis for this in literature or very little discussions of it anywhere, it's just something we've noticed time and time again when storms roll through at our coral farm.
Try to maximize your supplement dosing to optimize your pH stability (dose them at night) and be cautious when dosing medications or acids such as Selcon, Chemiclean, Nopox and be aware of the affect they will have on your system.