Milky looking water ?

Dear Lynn:

One thing that can cause a small closed-system aquarium to turn milky white is a sudden die off of a bed of Caulerpa due to stress or sexual reproduction. This can be harmful because toxins may be released by the Caulerpa in the die off and the resulting decay of a considerable quantity of vegetable matter can degrade the water quality and reduce the level of dissolved oxygen in the tank due to a bacterial bloom. In severe cases, this combination of events can stress the other aquarium inhabitants or even wipe out the entire tank.

But if the aquarium is well circulated, well aerated, and well filtered, even one of these dreaded vegetative events or Caulerpa die offs is more of a nuisance than a threat to the aquarium inhabitants.
As a case in point, consider the two-gallon tank I set up for photographic purposes when I did my first book on seahorses many years ago. This tank was lushly planted with an assortment of Caulerpa and other decorative macroalgae (Penicillus capitatus, Udotea, sea cactus, etc.) and heavily stocked with a thriving colony of dwarf seahorses. Sure enough, right in the midst of a photo shoot, the Caulerpa chose that moment to to die en masse, disintegrate and cloud the water. Much to my consternation, it turned the entire tank as opaque as a glass of milk in a matter of moments! At first visibility in the tank was perhaps an inch at best, but this gradually began to improve and after a period of several hours, the tank was crystal clear again. The primary source of filtration and aeration for that tiny tank was a simple, air-operated undergravel filter along with a considerable quantity of activated carbon, yet all of the dwarf seahorses survived the event with flying colors. In fact, one of the gravid males had given birth during the white out, and even the newborn fry were fine.

If you’re growing Caulerpa in your aquarium, Lynn, it can easily be prevented from going sexual and dying of simply by repeatedly pruning are aggressively thinning out the colony. This is accomplished by regularly plucking out excess fronds of the fast-growing Caulerpa; when you subsequently you remove the excess Caulerpa you’ve plucked out of the main colony, you’re exporting phosphates, nitrates and other nutrients from the tank, thereby helping to maintain good water quality, and pruning the runners helps keep it from going sexual.

When pruning or trimming back macroalgae, take care not to actually cut it. Remember, you’re not pruning hedges or trimming trees — the idea is to carefully pull up and remove continuous, unbroken fronds. Simply thin out the colony of excess strands, gently plucking up convenient fronds that can be readily removed intact. A little breakage is fine, but cutting or breaking too many strands will result in leaching undesirable substances into the aquarium water as the Caulerpa’s lifeblood drains away. Too much cutting or breaking can thus sap the colony’s strength and cause die offs or trigger the dreaded vegetative events that judicious pruning otherwise prevents.

If you’re concerned about your ability to maintain and control of Caulerpa properly, Lynn, just use a different forms of macroalgae that grows less rapidly instead and you can get the same sort of benefits at relatively little risk. In that case, some of the other macroalge you may wish to consider are Gracilaria, Ulva, Chaetomorpha, and Chlorodesmis. Hawaiian Ogo (Gracilaria sp.) are bushy red-to-brown macros that do well under low light levels. Sea Lettuce (Ulva sp.) are deep green sheets of algae that do best under a little stronger lighting. Maiden’s Hair (Chlorodesmis sp.) are bright green tufts or clumps of very fine-bladed algal mats to grow attached to small rocks. All of these types of macroalgae are much less prolific and slower growing than Caulerpa. However, like all macroalgae, they should still be harvested periodically in order to export the excess nutrients they have consumed.

Aside from red and brown Gracilaria and the bright green Ulva and Maiden’s Hair, some seahorse keepers also like the Chaetomorpha turf algae from <http://www.floridapets/&gt;. It can best be described as looking like the clumps of the colorful plastic grass we use to fill Easter baskets. It is popular because it is slow growing and doesn’t require the kind of pruning that Caulerpa needs, and because it it comes loaded with microfauna: miniature feather dusters, copepods and amphipods, tiny snails and micro stars. Sounds like another interesting marine plant that can add some extra variety to a lush bed of macroalgae.

In the meantime, try filtering your cloudy aquarium through a good grade of fresh activated carbon and be sure to increase the circulation and aeration/surface agitation on the aquarium until it clears up again. It would be prudent to perform one or more water changes to restore the water quality and remove some of the wastes released by the Caulerpa when it died off.

The recommended stocking density for large seahorses such as Mustangs and Sunbursts (Hippocampus erectus) is one pair per 10 gallons of water, Lynn. That means that an aquarium of 50-60 gallons would be the right size to support 5 pairs of seahorses or 10 large individuals comfortably. If you are relatively new to seahorses, then a 70-gallon aquarium would be a better choice since it would provide a little better stability and give you a greater margin for error.

Best wishes with all your fishes, Lynn!

Happy Trails!
Pete Giwojna