Considering Starting a 29g Seagrass/Shoal Grass Tank - Beginner Questions


New member
Hi All,

Let me start out by telling you a little about why I am considering starting up this 29 gallon seagrass tank. We currently have roughly a 300 gallon SPS reef system (220 display, 50 frag tank, 70 sump). This system does very well and utilizes high water flow, large protein skimmer, frequent (weekly) water changes and a calcium reactor. We also continuously run carbon and phosban reactors on the system. We have roughly a 1" crushed coral sand bed. I would like to utilize the SeaChem Gray Coast substrate to aid in maintaining our Magnesium levels without needed supplimentation. This substrate due to its dark color does not fit in with the main display system look/appearence.

As a result I am looking at plumbing in a 29 gallon (30x12x18) where I can use this substrate. I have also always wanted to do a nice looking planted refugium type saltwater tank so hopeing to accomplish this as well. I also am a clownfish breeder looking to get into other fish so considering a pair or trio of pearly jawfish and a banggai cardinal pair for the tank. This tank will be plumbed into the rest of the system.

My main questions are in regards to water flow, lighting and substrate composition for a seagrass type tank. Overall look for this tank is minimal rockwork with the full thing being seagrass much like where you would find pearly jawfish in the carribean.

What type of turnover rate should I achieve in this tank? Does it need strong random current (powerheads etc) or will surface/top flow from a return pump be sufficient?

What type of lighting? I have 2x65w PC lighting I could put over this tank or the preferred would be 2x24" VHO tubes (can run off a ballast already in use). Will this be strong enough for most of the type of seagrasses commonly kept?

What type of substrate? Will the SeaChem Gray Coast be sufficient? I have seen other planted tanks here on RC using it? I am planning about a 4" sand bed possibly even closer to 5" so the jawfish will be happy. Should I mix in and additives/muds to aid with the plants? I do not want to do anything that will harm/issue my SPS though either.

I am planning a 29 gallon tank over a 20 long because I figure this will give me still about 12" of depth after my sandbed is in place. Any other suggestions would be great. I would prefer not to have to dose the system with anything? The current system has a decent bioload so while nutrients are not overwhelming they are present in low numbers.

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New member
I don't think the 2x24 VHOs will be strong enough for seagrass. I'm not too sure about this, but I've heard a couple people on the board here saying that the only substrate that makes a difference is using decaying plant matter. I'd think this may create a lot of nutrients, but being spread out over 300 gallons may not hurt the SPS too much. 4-5 inches should be a good sand bed unless you wanted turtle grass. Of course I've personally failed both times I've tried to keep seagrass so my advice on the subject isn't the best, but it should be start.


New member
Will 2x24" VHO be enough for any decent macro algaes? I am not super hooked on needing this tank be seagrss or turtle grass was just an idea. I am not a big fan of macros that need a lot of upkeep like some caularapa that goes sexual.

The big things I am after with this tank is getting the grey coast substrate in the system and having it hold those couple pairs of fish. Since I already have the full reef I was thinking a macro/planted tank might be fun to try something different. Maybe this is not a good idea since my nutrients in the system are fairly low.


Premium Member
I think the 2 x 24 VHO will be enough as long as the tank isnt too deep. Get a low kelvin bulb 6500k - 10k.

What size is the grey coast sand? The fish will probably prefer a finer substrate like 1mm or smaller. Some seagrasses do better with a DSB of around 5-6 inches and I would recommend this for most if not all seagrasses. Once its set up get som livestock in there and let the sand bed mature for a few to 6 months minimum before adding the grasses especially if your not using a mud type substrate.

check out these articles:

Beyond the Refugium: Seagrass Aquaria
by Lardizabal, Sarah

Beautiful Seagrasses: Keeping True Flowering Plants in Your Marine Aquarium
By: Anthony Calfo