Excellent! A 75-gallon aquarium can certainly make a wonderful habitat for seahorses and I generally like the way you have equipped the tank, Lisa. The two Marineland Penguin biowheel filters, in conjunction with a DLSB and live rock will certainly provide your seahorse setup with very efficient biological filtration, including plenty of both nitrification and denitrification ability. With 70 pounds of aragonite in your deep live sand bed, you should have no trouble retaining the pH of the aquarium water in the proper range. And, of course, an in-tank refugium with an abundant population of copepods and amphipods is always a welcome addition to a large seahorse setup.
Give it its very efficient filtration system, your 75-gallon aquarium system can easily support two or three pairs of large tropical seahorses such as Mustangs or Sunbursts and still provide you with a very comfortable margin for error, Lisa.
Most of the current inhabitants of the 75-gallon aquarium should do very well with seahorses, Lisa. The pajama Cardinals, fire shrimp, red leg hermits, dwarf hermits, and Turbo snail all make good companions for seahorses. But you’ll need to keep a close eye on the scooters at first, and I recommend relocating the chocolate chip starfish as a precaution, as explained below:
When discussing compatible tankmates for seahorses, it’s important to remember that one can only speak in generalities. There are no unbreakable rules, no sure things, no absolute guarantees. For instance, most hobbyists will tell you that small scooter blennies make great tankmates for seahorses and 9 times out of 10 they’re right. But every once in a while, you will hear horror stories from hobbyists about how their scooter blenny coexisted peacefully with their seahorses for several months and then suddenly went "rouge" overnight for no apparent reason and turned on the seahorses, inflicting serious damage before it could be captured and removed.
Does that mean that we should cross scooter blennies off our list of compatible tankmates for seahorses? Nope — it just means that we must be aware that individuals within a species sometimes vary in their behavior and respond differently than you would expect, so there are exceptions to every rule. It’s fair to say that scooter blennies generally make wonderful companions for seahorses, but there’s always a small chance you might get Satan reincarnated in the form of a scooter blenny. There’s no guarantee that adorable scooter you picked out at your LFS because of his amusing antics and puppy-dog personality won’t turn out to be the blenny from hell once you release him in your seahorse setup.
In other words, Lisa, your two scooters are very likely going to be perfect gentleman and make fine tankmates for your seahorses, but observe them closely for the first several days after you add your seahorses to make certain that the scooter blennies do not object to their presence. After all, they will be the established residents in the aquarium, and the seahorses will be newcomers that are invading their turf.
As far as starfish go, it’s best to avoid a large predatory species such as chocolate chip starfish and African red knob starfish (Protoreaster spp.). I would describe predatory sea stars such as these as "opportunistic omnivores," meaning that they are likely to eat any sessile or slow-moving animals that they can catch or overpower. For instance, I would not trust them with snails, clams, tunicates, soft corals and the like. Most fishes are far too fast and agile to be threatened by sea stars, but seahorses are sometimes an exception due to their sedentary lifestyle and habit of perching in one place for extended periods of time. What occasionally happens, in the confines of the aquarium, is that a predatory starfish may pin down the tail of a seahorse that was perched to the piece of coral or rock the starfish was climbing on, evert it’s stomach, and begin to digest that portion of the seahorse’s tail that is pinned beneath its body. That’s a real risk with large predatory species such as the beautiful Protoreaster starfish are the popular chocolate chip stars, which are surprisingly voracious and aggressive for an echinoderms.
But there are a number of colorful starfish that do well with seahorses. Any of the brightly colored Fromia or Linkia species would make good tankmates for seahorses. However, bear in mind that, like all echinoderms, sea stars are very sensitive to water quality and generally will not do well in a newly established aquarium. Wait until your seahorse tank is well-established and has had a chance to mature and stabilize before you try any starfish.
Three attractive species I can recommend are the Fromia Sea Star or Marbled Sea Star (Fromia monilis), the Red Bali Starfish (Fromia milliporella), and the Red Starfish (Fromia elegans), which are safe to keep with seahorses. They are not nearly as delicate as the Linkia species and should do well in the tank such as you’re planning that has lots of live rock and optimum water quality, and are nonaggressive starfish that feed primarily on detritus and meiofauna on live rock and sandy substrates.
A protein skimmer should not be needed in a tank like yours that features plenty of denitrification ability, Lisa, providing you use a product such as AquaBella Organic Solution or SeaChem Stability on a regular basis to assure that the aquarium includes large populations of facultative and anaerobic bacteria that can complete the nitrogen cycle by converting nitrates into nitrogen gas, which will bubble out of the aquarium and be removed from the tank entirely. Adding monthly boosters of AquaBella, in particular, will be especially helpful for a tank like yours with a DLSB since it will help prevent any impaction of the gravel bed.
The beneficial microbes in the AquaBella rapidly undergo a population explosion in the gravel bed of the DLSB, taking advantage of the enormous surface area and virtually unlimited attachment sites it provides to build up their numbers quickly. These microbes utilize organic wastes as food, metabolizing organic solids and phosphates contained in fish wastes and leftover fish food as well as in detritus, enzymatically breaking them down to harmless substances in the process. This effectively keeps such wastes, organic matter, and other gunk from accumulating in the DLSB, preventing impaction and keeping the aquarium water crystal-clear while helping to maintain optimum water quality. (For hobbyists who might doubt the ability of beneficial microbes’ ability to rapidly breakdown the organic matter that accumulates in the substrate of a seahorse setup, I should point out that AquaBella is also used by hog farmers to break down the organic "sludge" that often accumulates in their hog pits to a depth of 2-3 feet over time. Needless to say, if the AquaBella can handle the tremendous amount of wastes produced by hogs being fattened for market, it will have little trouble keeping up with the waste products of your seahorses.)
In fact, the AquaBella is so effective in removing proteins and other organic wastes from the aquarium water that protein skimmers often have little to do in an aquarium that uses this product. Many times a protein skimmer proves to be unneeded for an aquarium that has been cycled with AquaBella and then receives booster shots of the bioenzymes it contains on a monthly basis. For these reasons, the AquaBella should be especially helpful in your 75-gallon tank with a deep live sand bed, Lisa.
As for what else you need before you bring in your ponies, Lisa, the two primary things that come to mind are the need to bolster your cleanup crew and the need to provide some colorful hitching posts for the seahorses. A selection of colorful branching corals and artificial gorgonians will provide convenient places for the seahorses to hang out and will encourage them to look their best and brightest. You can read a detailed discussion on the aquarium décor that is best suited for a seahorse tank in Lesson 1b (Decorating and Aquascaping your Tank) of the seahorse training program, which includes several dozen photographs of other hobbyists’ seahorse setups to give you a better idea of the possibilities in that regard.
Likewise, Lisa, Lesson 2 (Cycling a New Aquarium & the Cleanup Crew) of the seahorse training course will provide you with detailed recommendations for the type of sanitation engineers and aquarium janitors that are especially useful in a seahorse tank. You want to include more snails for one thing, including plenty of the Nassarius snails that make excellent sand sifters for a tank with a DLSB.
In short, Lisa, I would be very pleased to enroll you in the Ocean Rider seahorse training program and it will explain exactly what you need to do in order to convert your 75-gallon aquarium into an ideal biotype for seahorses, but the training program is a correspondence course that is conducted entirely via e-mail, so I need to have your e-mail address in order to get the lessons and information packets to you. If you will send me a brief message to the following e-mail address, I will respond immediately and include the lessons as an attachment to my e-mail:
Best wishes with all your fishes, Lisa! I hope to be hearing back from you via e-mail very shortly.
Happy Trails & Happy Fourth of July!
Pete Giwojna, Ocean Rider Training Program Advisor