rock or gravel

Dear hobby:

Okay, if you want to determine how much live rock is appropriate for your particular setup, then the dimensions of the aquarium don’t matter — just the amount of water it will contain. Don’t worry about compensating for how much might be contained within the filters or filtration system at any given time — just a rough guesstimate will suffice.

I was just discussing this issue with Tasha on this forum yesterday, so allow me to reiterate: As you know, as much as 1-2 pounds of live rock per gallon of water is recommended if you will be using the live rock as your primary means of biofiltration. That would be the MAXIMUM amount of live rock that you would ever want to consider for a seahorse tank.

In your case, your TruVu Aquasystem has an internal wet/dry trickle filter that provides wonderfully efficient biological filtration, so you don’t need nearly so much live rock. There is no minimum amount of live rock you should have in a seahorse tank such as yours, hobby. That’s strictly a matter of personal preference in a tank with a terrific built-in biofilter like yours. You can have no live rock at all, and the aquarium system can still be very successful.. Or you can have just a small amount of live rock to augment the filtration provided by the built-in wet/dry filtration system. That’s desirable because the live rock can provide denitrification, and complete the nitrogen cycle, converting nitrate into nitrogen gas which eventually leaves the aquarium. Denitrification is carried out by anaerobic (i.e., oxygen-hating) bacteria deep within the interior of the live rock, and that’s something that the wet/dry trickle filter cannot accomplish. A wet/dry filter will support a tremendous population of the beneficial Nitrosomonas bacteria that convert ammonia to nitrite, and an equally large population of the beneficial Nitrobacter microbes that then convert the nitrite into nitrate (both the Nitrobacter and Nitrosomonas are types of aerobic bacteria that thrive in the oxygen-rich environment provided by the wet/dry filtration system). But the built-in wet/dry filter cannot support any of the anaerobic bacteria that are so important for denitrification.

So the live rock complements a wet/dry trickle filter, which is extremely good at breaking ammonia down into nitrite and then converting the nitrite into nitrate, but causes the nitrate levels to steadily accumulate. This is where the live rock is important, since the oxygen-poor interior of the live rock harbors anaerobic bacteria that can go ahead and complete the nitrogen cycle, converting the nitrate into harmless nitrogen gas in a process known as "denitrification." Live rock therefore helps to keep the nitrate levels under control, at the low levels that seahorses need in order to thrive. And a certain amount of live rock will also provide the aquarium with stability by virtue of the additional nitrification and denitrification ability it offers.

Now, if you prefer artificial décor and you want to have no live rock or very little live rock in your tank, that’s just fine as long as you are diligent with your aquarium maintenance. Without the live rock, you will need to perform more frequent water changes and be diligent about harvesting macroalgae periodically in order to export nitrates from your aquarium and keep them within the acceptable range.

In your case, I would recommend selecting a handful of softball-size live rocks to provide some limited denitrification ability and extra stability for your aquarium. If you wish, you can place these at the back of the aquarium and conceal them behind the artificial decorations, so that they won’t detract from the effect you are striving to achieve with your aquascaping.

Or you could hand pick a few especially interesting formations of live rock to create a sort of interesting rockwork centerpiece for the tank — something with attractive arches, caves, or overhangs, and surround the rock formation with artificial decorations. You can always position artificial corals and synthetic marine plants in and on and amidst the live rock formation so that it blends in with the rest of your decor almost imperceptibly.

But that’s strictly a matter of taste. You needn’t have any live rock whatsoever in your tank if you are concerned about introducing pests or simply don’t like the appearance of the rock.

To help you decide if you want to include any rockwork at all in your setup, hobby, here is a post from another of our members (Sissy), in which she discusses why she likes to use live rock in her tanks in response to another hobbyist concerns:

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Well, personally I’m a big fan of live rock. Because of the massive quantities of beneficial bacteria that thrive both on the surface and deep within the substrate, LR is a great way of maintaining superior water quality. Commonly nitrate levels are kept lower in a tank stocked with live rock, since the bacteria needed to break down nitrate are anarobic and can live deep in the oxygen-poor sections of the rock. LR, of course, also provides a refuge for the copepod/amphipod population needed to keep a brace of seahorces and a dragonet or two. Finally, live rock provides some fascinating viewing experiences as time progresses. Most live rock will have creatures living deep within the crevices of the rock that start to sprout a few months after the rock is re-cured, including corals, coraline algae of course, and the occasional bit of sponge. Fresh live rock is even more varied in it’s livestock, but you run the risk of pest species sometimes.

If I may ask, why exactly don’t you want LR in the tank? Are you concerned with pest species? If I may offer a suggestion or two, there are a few ways to deal with the problems of pests on live rock. I’m not going to go into a curing lesson here — there are many different and excellent articles available online in regards to curing LR, and I won’t tell someone that one method is necissarily better than another. Let’s just assume you have your rock cured, or mostly cured.

First, and this is only my personal experience, but try to buy your LR from a LFS. You have the benefit this way of looking at the pieces and picking out exactly which ones you want. You can also observe the LR in the pet shop’s tank before you buy it sometimes, and watch to see if there are critters moving about it. You can also choose from most places how live the rock really is. My LFS is great, they have separate curing tanks for LR that is plain coraline-encrusted rock, some that is fully cured, near cured, and a tank for rock that is SO live it has lots of macroalgae, coral frags, etc, already heavily populated.

Second, if you choose your live rock and bring it home, you can always submerge the rock in a plastic container filled with RO/DI water. Many mobile organisms will flee the rock in a couple minutes of this exposure in attempt to find a proper saline environment. This includes pest bugs such as bristle worms and mantis shrimp. The downside of this is that if there are existing copepods on the rock, they will go too. This is less of a problem though because you can always re-seed the rock with fresh pods later. If you have the benefit of doing this in a white plastic container, you can also pick and choose the life that has fled the rock. In other words, if you see a crab or snail that you decide you want to keep, you can rescue it from the RO water and plop it in the tank for later.

Finally, go over the rock with a toothbrush, tweezers, and syringe with lemon juice. Remove any sessile organisms you don’t want with the brush or the tweezers. The dreaded Aptaisia anemones are pretty hard to see if the rock is out of the water, but if you do see them, or one sprouts later, you can inject them with the lemon juice. This is a trick I found online, and I’ve recently had the opportunity to try it. I’m happy to say that it is pretty effective! Use a diabetic syringe of 1 cc or .5 cc, and just inject .1 to .2ml of juice to the stalk or mouth of the anemone. It takes a day or two, but it works.

Well, I’m at the end of my speech here, so I’m getting off of the soapbox. It’s pretty evident that I am a fan of LR in a display aquarium of any kind, and I think you would find it easier than you expect to properly maintain your new dragonet’s and your sea horses’ food supply with the proper amount of rock in your tank. I’m no expert, this is just my opinion for what it’s worth. I’m just another schmoe with aquarium life constantly on the brain! :-))
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In short, you can have as much or as little live rock in your tank as you please, hobby. There is really no right or wrong way to proceed in that regard. First and foremost, you want to establish an aquarium that is aesthetically pleasing to you as the owner, since you will be spending so many hours observing the aquarium and you want it to be a showpiece for your home. If you don’t want any live rock at all in your tank, that’s cool. You’ll just have to be more careful about testing and controlling the nitrate levels in the aquarium, since wet/dry filtration systems are sometimes known as "nitrate factories" because of the wonderfully efficient nitrification they provide, along with a total lack of denitrification ability, leading to the buildup of nitrate. High nitrate levels can be harmful for seahorses when they get above 20 ppm, and they also can fuel outbreaks of unsightly nuisance algae, which are difficult to eradicate once they get a toehold in a new tank. But there are lots of ways other than using live rock to help keep your nitrate levels under control. Let me know if you would be interested in some tips for controlling nitrates and I would be happy to offer some suggestions for you to consider aside from live rock.

Best of luck preparing your new TruVu Aquasystem for seahorses, hobby!

Happy Trails!
Pete Giwojna