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Old 01-12-2009, 10:03 PM
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Myka Myka is offline
Join Date: Mar 2004
Location: Saskatoon, SK.
Posts: 11,266
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Natural seawater has varying levels of pH but is generally between 8.0 and 8.3. pH is the concentration of hydrogen to hydroxide ions in a solution. Do we care about that technical stuff? Not really. Let me explain...

I’m going to just barely touch on pH as it is a bit of a difficult thing to fully understand, and is affected by so many elements and situations that it would only be confusing to try to explain it all. The important part to know is that pH is affected by your alkalinity and magnesium levels, and also greatly affected by the acids produced when organics break down (nitrogen cycle). Another thing to note is that if your house contains certain levels of CO2 (much lower than is poisonous to humans) from you and your pets breathing in it, this can cause the pH to drop in your tank as the CO2 in your house mixes with the aquarium water. CO2 is acidic, this is why it is used to break down the calcium carbonate in calcium reactors. If you find in the winter your tank has a lower pH than in the summer this may be due to you not opening your windows for fresh air in the cold winter months, and having the levels of CO2 build up in your home. High aquarium temperatures also cause the pH to drop.

Many people struggle with low pH in their tank. This is often caused by a large amount of waste breaking down in the aquarium creating acids, or high levels of CO2 in the house (and hence in the aquarium). Low alkalinity can also be a factor, but on its own wouldn’t be the main culprit. Often you can raise your pH just by adding an airstone (or protein skimmer). The way I see it, is make sure your calcium, alkalinity, and magnesium are at acceptable levels, that your house and tank get plenty of fresh air, that you have a good protein skimmer and good circulation with powerheads to reduce the amount of waste breakdown in the tank (keep detritus suspended instead of settled), and your pH should gradually stabilize at an acceptable reading over the first 6-12 months the tank is setup. A fluctuating or low pH during the cycling of your tank is normal, and should correct itself after the cycle is finished and you have done a couple waterchanges, but may take a few months.

You may notice that your tank has a lower pH early in the morning than last thing in the photo period. That is normal. The organisms in your reef respire, and create CO2 at all times of the day and night. During the photoperiod the reef's organisms are using light energy to process CO2 and water into carbohydrate and oxygen. This process is called photosynthesis. As you know from reading above, as the levels of CO2 increase in the aquarium the pH drops, so when the lights are out, and photosynthesis is not happening there becomes an abundance of CO2 in the aquarium which causes the drop in pH at night. If the swing in pH is rather large, then you can add a refugium/algae chamber to your sump with chaeto, and run the lights on the refugium so they are on when the tank lights are off. Be sure the refugium lights don’t leak too much light into your display tank though.

My take on pH is leave it alone. Unless it is really out of whack, don’t mess with it. It is easy to change, but difficult to keep steady at a level that it doesn’t want to be at. This is one of those times where natural adjustments (fresh air, reducing organics, airstone, etc) is much more beneficial than chemical adjustments. A fluctuating pH level is much more detrimental to a reef than a low or high pH. If it is between 7.6 and 8.4 I say leave it alone, don’t screw with it. It ain’t broken, don’t try to fix it!

Waterchanges , Salinity, Specific Gravity, and Temperature:

Natural seawater (with the exception of the Red Sea and brackish areas) has a usual salinity of 35 ppt or specific gravity of 1.0264 which works very well in our reef aquariums.

Most of the corals we keep are collected from water which ranges from 82-86 degrees. Many people believe that we should mimick this, however our aquariums have limitations that aren’t expressed in wild reefs. The most important limitation is waste removal, which we do by filtration and protein skimming. Keeping high temperatures in our aquariums only achieves increased metabolic rates of the aquarium’s inhabitants which creates more waste. This is why a lower temperature of 76-82 in our aquariums is much more optimal.

When doing waterchanges get your fresh saltwater mixed up to the proper specific gravity and allow the water to circulate and match the temperature of your display tank with a powerhead and heater for 24 hours. It takes time for the pH of the new saltwater to stabilize, and aerating for 24 hours is a safe way to be sure of this. Retest the specific gravity after 24 hours and adjust as needed. Test the calcium, alkalinity, and magnesium levels with every new bucket of salt (roll the bucket several times to mix the salt before using it). Adjust as necessary with additives, then proceed with your waterchange. By doing your waterchanges this way, it is often unnecessary to dose your aquarium between waterchanges if you don’t have a high calcium and alkalinity demand, and do waterchanges often enough. This practise reduces the risk of overdosing your tank. It is good practise to figure out how often you need to do waterchanges to maintain your calcium, alkalinity, and magnesium levels without dosing your aquarium. However, it is impossible to maintain calcium and alkalinity levels in high demand reefs, and daily dosing will be required.


The number one rule for dosing is do NOT (like never, ever, ever) dose for anything you don't test for. That would be like filling your car with oil, and not checking the level. Too much and you blow the seals in your engine...too little and your engine will seize.

For large tanks, high demand, and/or mainly SPS tanks I would suggest the use of a doser. Some people with mid-sized tanks like to use Kalkwasser either by drip, a dosing machine, or a Kalk reactor/stirrer. Kalkwasser works quite well as it doses both calcium and alkalinity in proper ratio. Be aware that you will still have to supplement Magnesium when you dose Kalk. I personally do not like calcium reactors as I find they have a tendency to lower pH (by the use of CO2) and I feel dosers are easier to fine tune. Kalkwasser has the added benefit of increasing pH and is often dosed at night to compensate for the nightly pH drop.

There are also some two part solutions out there which can be setup as drips, on dosing machines, or dosed by hand. The two part solutions are made in complimenting saturation so that you use the same measure of each solution. This can be a very simple solution to calcium and alkalinity dosing especially for novice aquarists. When using Kalkwasser or a two part solution you will have to initially adjust your calcium and alkalinity with individual additives to the proper level, and periodically to prevent imbalance.

In the case of dosing there are some products out there that I feel are superior to others:

~ Two Little Fishies C-Balance (my first choice for liquid 2-part dosing)

~ Fauna Marin Calcium carbonate (my first choice for calcium dosing on any size tank)
~ Bulk Reef Supply Calcium carbonate (second choice)
~ Kent Liquid Calcium (for smaller tanks, pricey but easy to use)
~ Kent Turbo Calcium (for medium-sized tanks, or smaller tanks with higher calcium demand)

~ Fauna Marin Sodium bicarbonate (my first choice for alkalinity dosing on any size tank)
~ Bulk Reef Supply Sodium bicarbonate (second choice)
~ SeaChem Reef Buffer 8.3 (alkalinity dosing for sm/med tanks that tend to have low, high, or fluctuating pH readings)
~ SeaChem Reef Builder (alkalinity dosing for sm/med tanks with acceptable pH readings)

~ Fauna Marin Magnesium chloride used 8.5:1 with Epsom salt (8.5 parts MgChl and 1 part Epsom for balance)
~ Bulk Reef Supply Magnesium chloride
~ SeaChem Reef Advantage Magnesium
~ Littlesilvermax's Magnesium mix 8.5:1
~ Buy Magnesium sulphate (Epsom salt) in the pharmacy for mixing with Magnesium chloride. Mg sulphate is NOT acceptable for dosing solely.

~ RowaKalk Kalkwasser

For continued reading on these subjects check out Randy Holmes-Farley, the reef aquarium chemistry guru.

Feel free to suggest some additional information to the Guide, or if you have questions I can do my best to try to answer them.
~ Mindy

SPS fanatic.

Last edited by Myka; 11-10-2011 at 12:21 AM.