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sbcaes
05/09/2011, 08:45 PM
Seagrass Picos:
Has anyone here done them or read about it being done?
say in a fluval edge (6g). what issues if any would i run into?
im planning on keeping oar grass Halophila decipiens. and possibly some other macros.

thoughts? details?

sbcaes
05/10/2011, 02:48 PM
bump.

piercho
05/10/2011, 07:45 PM
I've kept stargrass, not oar grass, in a 65G tank 36X18, lit with 250W 6500K Iwasaki and lots of flow. Halophila of course smaller than other grasses and often from deeper water from what I've read so you may not need the intensity of light shoal grass, etc, might require. Halophila does not have a very extensive root system; IME stargrass got going quicker than other grasses and could grow in shallower areas of the substrate.

A problem with planted tanks not employing a sump is pH swing. Typically the pH gets very high at the end of the light cycle due to CO2 exchange with air lagging uptake in the tank. The more brightly lit and more heavily planted the tank the worst this is. Some inverts/plants will tolerate this, others not so well. Rather than try to ammend with CO2 injection I recommend overflow/sump. Overflow IME can do a good job of gas exchange which will moderate pH. Also marine tank buffer system very different from freshwater buffer system, and most marine plants like relatively strong water flows (at least compared to FW), all of which makes CO2 not that practical for planted marine tank, IMO.

An issue I never had but I've heard about from people keeping small seagrass tanks is the sand going sour with most of the depth being anoxic. Maybe a substrate heater like are used for FW planted tanks would help ammend this problem. The heated coils force advection in the substrate and help reduce anoxic zones. People will babble "you need more sand stirrers" but a) big stirrers not practical in small systems and b) micro-stirrers tend to get driven out of anoxic zones. In a strongly circulated 36X18 tank I never had this issue and most don't, but in small tanks with deep beds I think it may be a problem.

So, MY opinion here: seagrasses poorly suited for tank with small footprints and no OF. But oar grass a beautiful grass, and you won't know that you'd fail until you try. A 20G high tank with a 24 inch T5 fixture, an OF and a sump with 3-4 inch substrate would be the absolute smallest system I'd make a stab at keeping seagrass in, myself.

Amphiprion
05/11/2011, 11:47 AM
Interesting that you bring up the sand bed, as I had spoken to Dr. Ron about much of the same. He basically said that most critters would end up toward the surface, if not on the surface. I noticed mine trending this way when I allowed the grasses to overcrowd themselves. It also severely compacted the sand with extensive root and rhizome networks. In light of that experience, I think that regular pruning is absolutely essential--not only for the well being of the grasses, but of the tank/system itself.

sbcaes
05/11/2011, 04:44 PM
i'm branching out on a limb here. but what if one were to layer the substrate in a similar fashion to FW planted tanks. say... fertilizer/mud .5" -.75"layer and cover that with a .5-1" layer of argonite sand? and have a "shallow sand bed of sorts"

oar grass already doesnt have an extensive root structure. and the most ive ever seen it go into the mud/sand mixes ive had in the past (larger tanks), was about... 1"

maybe that could be a possible work around to the anoxious DSB depths?

i'm still trying to read up on how much of an issue ph swings will be for oar/paddle grass and havent seen too much info other than it might inhibit growth?

any other thoughts on how to make this project work?
as im pretty sure im pushing the limits of seagrass tanks in regards to size.

i'll also most likely be running the fluval edge fixture from nanotuners on this project.
which has an output similar to a 150mh-250mh.

Amphiprion
05/11/2011, 07:23 PM
i'm branching out on a limb here. but what if one were to layer the substrate in a similar fashion to FW planted tanks. say... fertilizer/mud .5" -.75"layer and cover that with a .5-1" layer of argonite sand? and have a "shallow sand bed of sorts"

oar grass already doesnt have an extensive root structure. and the most ive ever seen it go into the mud/sand mixes ive had in the past (larger tanks), was about... 1"

maybe that could be a possible work around to the anoxious DSB depths?

i'm still trying to read up on how much of an issue ph swings will be for oar/paddle grass and havent seen too much info other than it might inhibit growth?

any other thoughts on how to make this project work?
as im pretty sure im pushing the limits of seagrass tanks in regards to size.

i'll also most likely be running the fluval edge fixture from nanotuners on this project.
which has an output similar to a 150mh-250mh.

It definitely extends further than 1", but it isn't the 8 (and more) you can see with Thalassia. The rhizome network can get extensive if you allow it. It essentially solidified the sand bed in my old setup. I was able to remove it in 3 pliable sections, held together with Halophila roots.

pH increases can eventually halt growth, since CO2 would be limited and it also decreases the solubility of calcium carbonate, which would further limit things. I'm sure they have a high threshold, though, as they usually do with salinity and temperature.

As far as anoxia goes, it isn't just the roots, but the sheer amount of organic matter the grasses produce. It can literally suffocate everything, except for the absolute most tolerant organisms, leaving diversity fairly low.