First of all, let me just say that it sounds like you have an outstanding system for seahorses. A 55-gallon aquarium with a sump has enough water volume to provide stability and a comfortable margin for error. You’ve got outstanding biological filtration with a wet/dry trickle filter in addition to live rock, a nice assortment of macroalgae to make the seahorses feel right at home, and a good protein skimmer. I like the upgrades you’re planning with the addition of a canister filter and an ultraviolet sterilizer. The fishes and corals you are keeping are seahorse-safe companions that should not cause any trouble for your ponies.
I would be happy to discuss some ideas to further reduce your nitrate levels, Princess. In your case, since you already have a sump, I suggest modifying it slightly to create a two-chambered sump for your tank. This can be accomplished by installing a perforated tank divider across the width of the sump, thereby separating it into two isolated compartments. One side accommodates all of your equipment (in-sump skimmer, return pump, heaters, titanium grounding probe, UV sterilizer, etc.) while the other side can be used to establish a deep live sand bed (DLSB) with plenty of Caulerpa. The DLSB/Caulerpa side will serve as a refugium and will soon become populated with countless critters (copepods, Gammarus and other amphipods, larval crustaceans, etc.). With the Caulerpa acting as an algal filter and soaking up nitrates, along with the anaerobic layers of the DLSB providing denitrification, the aquarist never need be concerned about nitrates or nuisance algae with this type of sump/refugium.
A lush bed of macroalgae in your sump, including fast-growing Caulerpa along with perhaps some Chaetomorpha and assorted Gracilaria macroalgae could also make a huge difference. Those macros don’t require strong light to thrive; and would do very well under 4-6 inch incandescent bulbs in a simple strip reflector or ordinary daylight fluorescent bulbs. I would situate a good bet of such macroalgae n your sump directly under the lamp, and then keep them illuminated 24 hours a day right around the clock.
That will accomplish several beneficial things: for one, keeping the lamp lit continuously will help prevent the Caulerpa from going sexual. Another big advantage is that it will encourage vigorous algal growth and harvesting some of the macroalgae regularly will export large amounts of excess nutrients (nitrates and phosphates) from your tank.
Finally, operating the lighting in your sump around-the-clock will further increase the stability in your tank by helping to offset the daily fluctuations in pH, photosynthesis, dissolved oxygen/carbon dioxide, and redox levels that otherwise occur in the aquarium. Daily variances in chemical, physical and biological phenomena are a fact of life in aquaria, linked to the light and dark cycles and the diurnal rhythms of captive aquatic systems. As one example, the pH of aquarium water typically peaks after the lights have been on all day at a maximum of perhaps 8.4, only to drop to low of below 8.0 overnight. This is related to photosynthesis and the fact that zooanthellae and green plants consume CO2 and produce O2 when there is adequate light, but in essence reverse that process in the dark, consuming O2 and giving off CO2. Redox levels, available calcium and other water quality parameters are affected in similar ways. Needless to say, these variations are far greater is a small, closed-system aquarium than they are in the ocean, so it’s beneficial to minimize such fluctuations by maintaining 24-hour illumination in your sump. Voila! Just like that the roller coaster ride is over: no more daily fluctuations in pH or highs and lows in calcium levels, oxygen minima, or peaks and valleys in redox potential.
Denitrification is the process by which anaerobic (oxygen hating) denitrifying bacteria then convert nitrate into completely harmless nitrogen (N2), which eventually leaves the aquarium. Denitrification thus removes nitrate from your system. A deep live sand bed (DLSB) thus helps reduce nitrates because anaerobic denitrifying bacteria can flourish and break down nitrates at a certain depth below the sand where oxygenated water no longer penetrates.
If you use fine enough sand in your DLSB so that detritus remains on the top and cannot migrate down into the substrate, then you really don’t need any sand sifters at all other than the microfauna that come to populate any sandy substrate. I recommend sugar sized sand grains, or something finer still. A depth of 5-6 inches should be more than sufficient, and with a DLSB and a good growth of macroalgae, you should never have to worry about the nitrate levels in your aquarium.
For additional information on setting up and maintaining a DLSB, check out the following FAQs site by the wetwebmedia guys. Skim through it carefully and it should give you lots of good ideas regarding how to proceed:
Click here: DSBFAQs
You mentioned that you were keeping polyps in your 55-gallon aquarium, Princess, which is just fine. They are hardy, attractive, fast-growing corals that are perfectly safe for seahorses, but I just wanted to remind you should be sure and observe the necessary precautions when handing such colonial polyps and placing them in the aquarium.
First and foremost, many of the commonly available Zooanthus (button polyps) and Palythoa (sea mats or colonial polyp) species contain a very toxic substance in their mucous coat known as palytoxin, which is one of the most poisonous marine toxins ever discovered (Fatherree, 2004). Palytoxin can affect the heart, muscles, and nerves, resulting in paralysis or possibly even death, and many hobbyists have reported numbness, nausea and/or hallucinations after merely touching these corals (Fatherree, 2004). When you handle zoanthids and palythoans, you cannot help picking up some of their protective slime on your fingers, and so much as rubbing your eye, picking your nose, or a small cut on your finger can be enough to land you in the hospital. When handling Zooanthus or Palythoa species, it’s very important to wear disposable latex gloves, avoid touching your mouth or eyes, and carefully dispose of the gloves immediately afterwards (Fatherree, 2004).
Secondly, zoanthids and other soft corals such as your pulsing Xenia may wage border battles if you place them in close proximity to each other. So be sure to allow adequate space between the colonies. Some rapidly growing polyps and Zooanthus colonies can be aggressive to soft corals as they rapidly spread over the rockwork, but in general they are quite peaceful, and you can always slow down their rate of growth by reducing the nutrient loading in the aquarium.
As an added precaution, it might be a good idea to get a good grade of activated carbon that’s low in ash and free of phosphates, add a couple of ounces of it to your canister filter, and replace the used carbon with fresh, clean activated carbon once a week. (If you don’t replace the activated carbon regularly, it can leach back any undesirable substances it has removed into the aquarium after it has reached its capacity.) The activated carbon would eliminate any possible concerns about the polyp’s toxins build enough in the aquarium by removing them from the water.
Carbon is activated two ways, either with steam or with phosphoric acid. The type of carbon that is activated with phosphoric acid contains phosphates, which can be leached back into the aquarium water and promote the growth of nuisance algae. So you will want to avoid that type of of activated carbon. The carton or box that the activated carbon comes in should be clearly labeled and state specifically that it is "steam activated" or "phosphate free" or something to that effect if it’s a suitable brand for your aquarium.
We’ve had other discussions on this message board from seahorse keepers who are having problems with nuisance algae and needed help reducing nitrates in order to get the nuisance algae under control. If you look up the following thread titled "hair algae," you’ll find lots of other suggestions for lowering the nitrate levels in your seahorse tank, Princess. You can read through those ideas online at the following URL:
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:hair algea – Ocean Rider
Best wishes with all of your fishes, Princess! Here’s hoping that Precious will be pairing up with a new Sunburst stallion before you know it!