In our 20th episode of the 52 FAQ, we are answering Mack Jones question from week 13: "When Marine Pure Ceramic Biomedia plates are substrated in the sump without water flowing through them, wouldn't they just become anaerobic filters over time? Why not save $500 and just have a deep sand bed for filtration?"
Those are two pretty hotly debated topics wrapped up into one question. Deep sand bed’s and marine pure in general provide an environment capable of converting nitrate into nitrogen gas. Even if that was the case, I think most people are going to be happier with the marine pure blocks and I will share why.
First I have seen enough deep sand beds that have been effective at processing and essentially removing nitrate so this is a legit question. For those of you that are not familiar with deep sand beds, they are typically 6-8" deep beds designed to promote an anaerobic area in the tank where there is little to no oxygen. the bacteria that populate this area utilize oxygen found as part of the nitrate molecule for biological function and release the free nitrogen to bubble out of the tank.
On occasion you will see deep sand beds being implemented in new setups, however popularity has dropped. Frankly, it’s not the most attractive look for a tank and there are a whole slew of ways to control nitrate now days without all that sand in the tank. It’s also super hard to remove and serves as a giant detritus and nutrient sink, potentially even a contaminant sink and has the potential to become toxic over time. I would go as far as saying some reefers feel like they are more or less a nutrient or contaminant time bomb where one day they could be the cause of algae outbreaks, coral mortality, or even a complete crash.
Now that last part can’t be confirmed and I guess I don't have an opinion one way or another, outside of the fact that it is very obviously a detritus trap, but long term negative outcomes been stated enough times that deep sand bed’s are a pretty big rarity these days.
To help combat some of these issues many reefers started making remote deep sand bed’s, or like Mack mentioned just fulling the refugium area with a deep sand bed. There are the same benefits and issues when placed remotely but the biggest benefit is you can remove the sand every few years and replace it or clean it much easier from a remote location compared to in the actual tank. And of course you don't have to look at all that sand in your tank, with valuable real estate taken up by a large volume of sand.. I will also say sand isn't cheap either. To do this properly we would have to use a couple hundred dollars in sand as well.
So why marine pure instead? So many aquarists theorize the same thing happens inside the marine pure blocks as well. we have never confirmed that with actual testing but the brs team has certainly heard enough anecdotal evidence to this point that there is a very good chance the marine pure blocks are achieving the goal of creating anaerobic zones, where the transition from nitrate to nitrogen gas is happening and reducing the nitrate levels in your tank.
The marine pure blocks are extremely porous. The material itself has about double the surface area per gram over reefsaver and pukani and about the same as fiji. However where it differs is how that surface area is an interconnected network of pores.
some of you may have already seen this demo where we glued a plumbing fitting to the top of a block and you can see how water just runs strait though the network of pores within the marine pure.
So when placed in a low flow area like the bottom of a fuge it is theorized that it allows enough water to flow through to process the water efficiently but the aerobic bacteria on the surface layers strip the oxygen out to create an anaerobic center. Hard to know if you need a thick block to do that or even that can happen in the smaller balls or even plates. I am going to give you a sneak peek into the future, but this is something we are going to test in the not to distant future and share with you.
I will note that some reefers have claimed that the type of ceramic that marine pure is made from can release small amounts of aluminum into the tank. I guess I can’t confirm that and I don't think anyone has definitively shown this is a major issue regardless. I can say that results are results and I have never seen a negative reaction, many of the tanks here at BRS use them and the reviews from customers who actually use them are overwhelmingly positive. Like everything there is upsides, downsides and a handful of unknowns to every approach.
End of story, the reason I would suggest the marine pure over a deep sand bed is in most installations it is going to cost about the same as buying all that sand, way easier to install and doesn't require all that maintenance. Overall I think the long term risks to the tank with a deep sand bed are substantially higher.
A couple tips with marine pure, make sure to rinse it prior to use to get all the dusty fines off that are created during transport. The material is also fairly fragile so I would place it in an area where it is unlikely to get disturbed often. if you are using it for normal biological cycle to back up or support your live rock you can put it in high flow areas. If you want to use it to reduce nitrate I would put it in fairly low flow areas like the bottom of your sump.
If you are interested in learning more about the cycle or natural methods or removing nitrate check out Week 13: Ammonia, not as simple as you think: the ideal tank cycle or Week 26: How to leverage bacteria for a cleaner reef tank. Don't forget answering your questions is what the 52 FAQ is all about on so ask us something you want to know in the comments down below. See you next week with the next 52 FAQ!
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