Yes, I would say sponge filters are probably the best option for Pixies or dwarf seahorses (Hippocampus zosterae). Second-best would be a set of undergravel filters that completely cover the bottom of the aquarium combined with a calcareous gravel substrate.
Small power filters are problematic because of the small size of Pixie tanks, which are often 1-5 gallons, and the fact that they tend to suck up and filter out all of the newly hatched brine shrimp which the Pixies require in copious amounts on a daily basis. In order to prevent that from happening, you must screen the intake for the power filters very well using a coarse sponge and turn down the flow, which essentially transforms the power filter into a glorified sponge filter and sometimes causes problems with clogging and overheating in the process and can shorten the life of the power filter. You are generally better off and ahead of the game if you use inexpensive air-operated sponge filters to begin with, or alternatively, a foolproof undergravel filter.
No, sir, a goldfish bowl is not really what you need for hatching out brine shrimp for your Pixies at all. You’ll need to set up an array of at least two brine shrimp hatcheries so you can hatch out more baby brine shrimp each day before you run out. Many commercially made hatcheries are available or you can easily improvise your own from 2-liter soda pop bottles or quart jars. Fill the jars or bottles about 4/5 full with saltwater and equip each container with an airstone connected to a length of rigid airline tubing that reaches all the way to the bottom. An inexpensive vibrator air pump with a set of gang valves with put out enough air for the entire battery of hatching containers. Add 1/8-1/4 teaspoon of brine shrimp eggs to each container and adjust the valves so the airstones bubble vigorously, keeping the eggs in suspension at all times. Shine a light directly on the hatching bottles and keep them illuminated 24 hours a day.
The eggs will begin hatching after 18-24 hours, and the emerging nauplii should be harvested and used as soon as possible after incubation while they still retain their full nutritional value. (The yolk supply lasts about 1-2 days after hatching, and the food value of the nauplii deteriorates steadily as the yolk sac is consumed. Once it has been exhausted after about 48 hours, the nutritional worth of the nauplii drops drastically.)
However, before they can be used as food, the nauplii must first be separated from the indigestible egg shells. Otherwise the empty shells may be accidentally ingested by the seahorses, which has been known to cause intestinal blockages and death.
The brine shrimp nauplii can be separated from the eggs simply by turning off the air for a few minutes and allowing the water to settle. The unhatched eggs will sink to the bottom of the hatching jar while the empty egg shells will float to the top. The nauplii can then be concentrated in the center of the jar by darkening the room and shining a flashlight on the jar’s midsection. (Brine shrimp are attracted to light and will be drawn together in midwater where the light is focused.) Harvest the nauplii by using a siphon or turkey baster to suck up the concentrated mass of shrimp. The shrimp-laden water can then be strained through a plankton screen or fine-meshed brine shrimp net.
Return the strained water to the hatching container, add more eggs, and readjust the aeration. The same hatching solution can be used for a week’s worth of hatchings before it has to be replaced.
Alternating the hatching container from which you harvest each day’s supply of nauplii will assure that you have a nonstop supply of newly hatched brine shrimp available at all times. For best results, you should decapsulate the cysts before hatching them, as explained below.
If you’re still uncertain about how to proceed, geek, the information at the following links should make everything perfectly clear:
Click here: Hatching Brine Shrimp
Good homemade hatcheries here:
Click here: Culturing Brineshrimp
Click here: Brine Shrimp Technical Information 1
The depth of the sand substrate does not matter in the least for Scarlet Reef Hermit Crabs (Paguristes cadenati) since they don’t burrow. Nassarius snails do burrow and will appreciate a bed of fine-grained live sand 1/2 to 1-inch deep.
I use sand in all my seahorse setups and I have never had any problems. I find that a fine-grained oolitic live sand, preferably black, helps control nitrates and looks great, as discussed below.
A thin layer of live sand is the ideal substrate for a seahorse tank. It is bioactive, aesthetically pleasing, and is a fine-grained sand well suited for the various snails that form an essential part of the cleanup crew for a seahorse tank. I find the dark color of an oolitic black sand substrate shows off my seahorses and macroalgae to great effect and enhances the appearance of tank in general. (As long as it’s fine enough I’ve never had any problems with seahorses "snicking" up sand in the aquarium. They will do so on occasion when feeding off the bottom, but never have any difficulty at all expelling it again as long as it’s fine grained.)
The depth of a shallow sand bed like this is a crucial factor. Too deep, and you risk anaerobic dead spots where deadly hydrogen sulfide gas can form. Too shallow, and there will be less surface area to support beneficial nitrifying bacteria and Nassarius snails and other beneficial burrowers may feel vulnerable and exposed. A bed of live sand between 1/2 to know more than 1-inch deep is just right for the main tank.
The types of live sand I prefer are either the Arag-Alive Indo-Pacific Black Sand by CaribSea or else the CaribSea Tropical Isle Tahitian Moon Black Sand. You can obtain them online from Premium Aquatics and a number of other sources, and either of them should work great for your dwarf seahorse setup.
Fine-grained oolitic sand tends to keep fecal pellets and other debris right on top, where it can easily be removed by vacuuming the sand or carefully siphoning off the bottom when you perform water changes.
Pre-aged saltwater and live sand do contain enough beneficial bacteria to help seed your tank with nitrifying bacteria while it cycles, but by no means will they provide your tank with instant biofiltration ability. You will still need to cycle your Pixie tank and build up a thriving population of the beneficial Nitrosomonas and Nitrobacter nitrifying bacteria to establish the biofiltration before it can support seahorses are any other life. As we have discussed before, it can take anywhere from 3-6 weeks to cycle and aquarium from scratch this way, depending on how you go about it. Using pre-aged saltwater and live sand can help accelerate the cycling process, but they do not eliminate the need to cycle your courting and establish the biofiltration. Do not order your Pixies until their aquarium has been completely cycled.
You can combine pre-aged saltwater and newly mixed saltwater freely without any problems. That will not harm what if you beneficial bacteria are present in the pre-aged saltwater. The beneficial nitrifying bacteria that provide the biofiltration for your aquarium require a substrate of some sort, such as a sponge filter or other biological filter media, to attach to and are very rarely simply suspended in the water.
Best of luck with your new Pixie setup, sir!