Q. I have had a reef tank for several years and would like to start spawning my corals, clams and anemones. I have read everything I could find online and think my system can be successful. I plan to vary the lighting over the course of the year, so I will have a season with longer photoperiods and a season with shorter photoperiods. I will use a moonlight timer to simulate moonlight and plan to vary the temperatures over the course of the year. What do you think so far?
-- Bill Mahoney

A. Bill, it sounds as if you have all the physical bases covered for sure! It would be nice to know what corals you plan to spawn because this would have a lot of bearing on requirements to rear the offspring and which techniques to use to collect the gametes or planulae.

There are still several factors to consider first. For example, several corals are broadcast spawners (they release eggs, sperm or egg/sperm bundles into the water, where they combine and fertilize to form embryos and, eventually, planulae). In most of these cases, you need to have separate genetic colonies because many of these corals are not self fertilizing. In some cases, a coral is gonochoristic, meaning there are separate male and female colonies (e.g., Euphyllia). So, you would need to have both sexes in the same aquarium.

In my experience, however, the biggest problem you will have is that the broadcasters will release their gametes en mass, which will have a negative impact on the tank’s water quality because millions of sperm and eggs can be produced in one evening. The biggest resulting issue is the depletion of oxygen in the water — oxygen levels can rapidly fall, resulting in fish moralities.

At the Waikiki Aquarium, we have an exhibit of anemones. It is about 350 gallons and contains several dozen Entacmaea quadricolor (bulb-tip) anemones, two Stichodactyla gigantea and one S. mertensii. There are also more than a dozen Amphiprion ocellaris, a pair of Centropyge bicolor (12 and 7 years in captivity, respectively) and a Chelmon rostratus (10 years in captivity). The tank is an open system with a small circulation pump and a few air stones.

In March, the bulb-tipped anemones released huge quantities of sperm one night, as they do each year. The next morning, the water looked as if someone had poured milk into it — you could not see the bottom! The fish were breathing rapidly, and several were resting on the bottom. A 50-percent water change was performed immediately, and the incoming water flow was increased. Another air stone was added. Unfortunately, we lost the younger bicolor angel. This occurred for two more nights in a row, but because we left the extra air stones and kept the incoming water flow high, we did not lose  more fish. I hate to think what would have happened if this were a closed system.

Thus, I tend to discourage people with closed system reef tanks from encouraging a mass spawning of corals, clams or anemones. Unless you can be there when it happens and can predict exactly when it will occur (not impossible, but not easy, either), and unless you can perform massive water changes in a short time, it is a dangerous event to happen in an aquarium.

Cyanobacteria problems
Q. Would you please help  identify this algae in the photos I’ve sent? (Photos are not shown here. —Eds.) I think it may be Bryopsis. All water parameters are within specs, except nitrates at about 10 ppm. I am also having trouble getting the pH up to 8.0 or above. I added crushed coral to the substrate of “Arag-Alive” Fiji pink live sand, but the pH still won’t reach above 7.6. When I first set up this tank about six months ago, I added some live rock.
-- Michael D. Cregar

A. The pictures you sent show some cyanobacterial growth, but not Bryopsis (a green fluffy algae resembling a bundle of featherlike tufts that can reach a couple inches long.

Cyanobacteria appear when nutrient levels become elevated, especially phosphate. It is not uncommon to have growth of cyanobacteria when an aquarium is first established, because nutrient levels can become elevated in the beginning, particularly when using new live rock. You don’t mention anything about filtration, lighting or tank management practices, so it really is impossible to troubleshoot your system.

Is this a reef tank with corals or a tank with just live rock and fish? If you do not already have one, I urge you to purchase a protein skimmer. These remove a large number of compounds from the water and have a positive impact on water quality. I would also take a look at the quality of freshwater you use to replace evaporation and mix new saltwater, because the source water can sometimes have elevated levels of phosphate and nitrate, as well as other plant/algae nutrients.

You should be measuring calcium, as well as alkalinity levels, because these are closely tied for maintaining pH. Adding crushed coral will do little to raise the pH much above 7.8 or so; its main role is to act as a buffer against pH that is too low. If you use a test kit to measure pH, you might want to buy fresh reagents to ensure a correct reading. If using a pH probe and meter (the recommended method, usually available for less than $90), make sure the probe is less than 2 years old and has been calibrated recently.

You should do several things to raise pH. First, get alkalinity into the range of 2.3 to 3.5 meq/L through the addition of buffering compounds. This will help reduce fluctuations in pH over the course of the day. The buffer will also contain compounds that will help raise the pH.

Second, make a solution of calcium hydroxide and water (kalkwasser) to replace water lost via evaporation. This will have a high pH that can help reduce phosphate, will aid in the conversion of carbon dioxide into bicarbonates (which will help to boost alkalinity) and will neutralize acids produced by biological activity in your tank, thus raising pH.

If the levels are correct for alkalinity and calcium, and you are using a protein skimmer but still have low pH, then this may be a sign of excess carbon dioxide in the water, which acts to lower pH. This could be due to poor air ventilation in the room, a tight-fitting tank cover or the aquarium being in a crowded room. One way to test this is to place an air stone in the aquarium, and aerate the water vigorously. If the pH begins to rise in just a few hours, it’s a good sign there is a carbon dioxide problem.