I am a bit of an aquarium geek or fish geek, whichever term fits best. I’ve had a 6 gallon Marineland Eclipse6 acrylic tank on my den desk for nearly 8 years now. I have kept a variety of freshwater fish with some driftwood planted with Java Fern and Anubias. It hasn’t been a bad aquarium and has served its purpose fairly well. The pump, filter, and bio-wheel have been okay but nothing spectacular. What can you expect for a small 6 gallon complete system? At this point, however, the acrylic has taken a beating with my kids and is really showing its age with a lot of visible scratches and marks. The acrylic has also displayed what looks like cracking in a few spots that has me concerned it will randomly spring a leak one day. So, I’ve decided I’ll be proactive and replace the tank. After all, I need to have an aquarium and so do the fish.
So, I went to several fish stores and looked around online and I discovered these “nanocube” systems from a variety of manufacturers that are right in line with what I was looking for. The primary target for these nanocube products is for people who would like small saltwater or marine reef systems, but they will work perfectly for freshwater, as well. Most of them include all the necessary lighting and cooling and a full 3 stage sump system. The system I ended up selecting is the CoraLife BioCube 14. It was previously branded by Oceanic, which, if you aren’t aware, was THE brand name in the custom glass and acrylic aquarium industry. It was the benchmark that all aquariums were measured against. Sadly, the Oceanic brand has all but disappeared now, due to corporate changes the parent company decided to make. Many, if not all, of the expert tank builders that used to work for Oceanic, here in Dallas, went out on their own and formed Deep Sea Aquatics (DSA) which has been successfully earning the old reputation that Oceanic had. If I had unlimited funding, I’d have them build a custom bowfront tank for me, similar to the Extreme Bowfront 180 to fit between my bookshelves in my den. A geek can dream, can’t he?
The CoraLife BioCube 14, as its name suggests, is mostly cube shaped and approximately 14 gallons in size. In reality, it is more like about 12 gallons in actual water volume minus any displacement for substrate and decorations. It is similar to the game TV manufacturers play with the sizing of TV screens. About a gallon and a half of space is dedicated to the 3 chamber sump system at the back of the tank, so the functional space for the fish is even less. When the system is running, the 3rd sump chamber with the pump will only have a max of about 5 inches of water depth in it. This leaves nearly a third of the sump space empty. The water level also can not rise above the top rim based on the overflow design which eliminates another inch of water depth. So the tank would be 14 gallons if you measured using the outside dimensions of the tank. At 15″ x 15.5″ x 14″ that comes out to roughly 3,255 cubic inches which equates to 14.09 gallons. The inside dimensions of the functional aquarium space come out to 13″H x 12″ D x 14.25″ W. This works out to 2,223 cubic inches which is the same as 9.6 Gallons. The sump space will hold approximately 1.7 Gallons. So, for your reference, the BioCube 14 system will have an actual functional water volume of around 11.3 Gallons.
The pump is the Coralife S-700 which draws 10 Watts of power and rated at 180GPH. It isn’t top of the line but will do the job. I did a quick search just for comparison and I found another pump by Cobalt Aquatics that would fit for ~$36 retail or $26 on Amazon that draws 8.5 Watts (runs cooler) and can push 230GPH. This is an option if heat is an issue from the pump or you want even greater water movement. At 11.3 Gallons of water volume in the tank that means the pump can turn the tank over almost 16 times an hour. That is way more than the 4-5 times necessary for a heavily stocked and planted freshwater tank. Since these systems are targeted at the saltwater/reef community, they must have a pump that can generate enough water movement to keep the corals healthy. For someone putting together a freshwater tank like mine, the bonus is that the high rate of water movement should really help with plant growth and the system should stay pretty darn clean, not to mention the fish who are really active swimmers should enjoy the current.
The BioCube 14 comes with an integrated lighting system in the hood, designed primarily towards saltwater/reef systems. The hood has a small hinged feeding lid at the front and the entire hood is hinged so you can easily lift it for access. The hood’s hinge pins are removable, so that you can remove it completely when needed. There is an included 24 Watt Actinic Blue fluorescent light, along with the standard 24 Watt 10K Daylight fluorescent, as well as .75 Watt moonlight LEDs. There is a slot for an additional LED bar if you choose to add one. Each fluorescent bulb has a separate power cord and light switch. The LED bars are all tied to the same power cord, so they can only be manually alternated using the switches between daylight and moonlight. There are also fans to force air through the hood to keep it cool while the lights are running. The fans are wired to the “PC1” slot in which mine had the Actinic Blue light installed. I guess the assumption is that the Actinic Blue light generates the most heat, so they tie the fans to that bulb being on. In my case, I don’t need the Actinic Blue light since I am not growing coral. However, I do want the fans to run when the 10K bulb is on to eliminate as much heat as possible. I have to test if I can just remove the Actinic Blue bulb and still run the fans or if it is in-line and requires the bulb to be plugged in and turned on. If the bulb is required in the slot, I will just move my 10K bulb into that slot and run it that way.
I did my initial water test just to verify that the tank was sealed properly and no leaks were present. I had done some reading that mentioned that the sump chambers might not be well sealed from each other out of the box. So, I wanted to make sure before I put it all together and found out the hard way. I filled the main tank up with tap water to just below the bottom sump overflow and let it sit for a while. I did not discover any leaking from the main tank to the sump nor any leaks around the base, so that was good. I dumped it and then filled water into the 1st sump chamber and I immediately noticed that water was slowly leaking to chamber 2 along the front edge toward the main tank. So I slid the tank over the edge of the counter so I could look underneath, since it is clear glass, and I could see that the black silicone seal at the base of the 1st chamber did not completely join with the seal along the front edge to the tank. This isn’t the end of the world or earth shattering by any means. The tank will still work fine. It just means that some water will be leaking through and bypassing the filters. Being the perfectionist that I am, I do not want that. So, I’m going to fix it.
So that begs the question, what kind of silicone do I use to fix it the right way and not introduce any toxic substances to the tank? I did some reading on this subject, since I am building a custom background for the tank and need to silicone it into place. I found all kinds of raging debate on this topic. One thing is for sure, some silicone is a “sealant” and some silicone is an “adhesive”. There is a big difference between the two. Silicone sealant is fine for placing things in the tank that you want to stay more permanently. However, silicone sealant is not what you want to use for any high pressure joints like when building an aquarium. That job requires a true adhesive that is much stronger. Most local fish stores will carry some sort of silicone sealant makred as “aquarium safe”. These silicone products are usually specially packaged, clear/translucent, and twice or even three to four times the price of the typical silicone you might find at the hardware store. I did find Home Depot had a DAP branded package of aquarium sealant in one of the paint aisles near the resins and Bondo and it was a smaller tube similar toothpaste that was in the $10 range. Not only are they expensive, remember these are sealants and not adhesive. So, don’t go building your own custom tank with it. In a larger tank if you are sealing an overflow box, plumbing, or even a decorative background, you should really use a silicone adhesive and not just a sealant. You’d rather be safe than sorry.
So, that still doesn’t answer the question. What silicone adhesive product should you use for a fish aquarium? The answer that I’ve found is a product made by the manufacturer of all of GE’s silicone products that you find in the hardware stores. The product is Momentive RTV 103 or 108. RTV just stands for Room Temperature Vulcanizing. In other words it is a 1-part silicone compound that cures at room temperature without heating or cooling. RTV 103 is black and RTV 108 is clear/translucent. This product is supposedly what most aquarium manufacturers use to build their aquarium joints, since it is a very strong adhesive silicone. It uses Acetic acid in its curing process which I’ve read is the safest option in an aquarium. Silicones that release ammonia and/or methanol as part of curing are unsafe for aquariums. Momentive RTV 103 and 108 also do not have any mold or mildew resisting additives in the compound. These additives, such as Bioseal, are typically a type of fungicide and usually have a biological impact that is toxic to the aquarium environment. They are found in many of GE’s and most other brands typical consumer grade silicone products.
This is where I found the largest amount of debate. Supposedly, GE Silicone I Clear/Translucent Door & Window 100% Silicone (manufactured by Momentive) which can be found in most hardware stores for less than $6 a 10.1 oz tube does not include any of these mold and mildew resisting additives either. However, GE has started marking these packages with specific notes stating that they should not be used below the water line or in aquariums. The belief is that this is just a legal disclaimer, since it is a sealant and not an adhesive. The idea is that GE is just trying to avoid liability for any lawsuits where someone uses this product to build a big aquarium and the joints fail or spring a leak because of too much pressure and not a strong enough adhesive. However, GE is now claiming, according to a statement one person received when talking to a representative, that any of their typical consumer silicones (I or II) can contain trace amounts of the mold and mildew resisting additives, whether the package is marked or not. There are many claims that this is bull and just tactics they are using to scare you into buying the specially packaged product that is 2-4 times more expensive. I’ve tried reading into the Material Safety Data Sheets and I’m not finding any obvious indicators one way or the other. According to an unverified statement from a GE chemical engineer, the formulation of GE’s Silicone I product is identical to the one used in specially marked “aquarium safe” packaging. There are many claims as recent as 2013 that I found where individuals have used the regular GE Silicone I in their tanks and have had no issues with it.
At this point, I decided to just go with the black Momentive RTV 103 product to seal the sump. I don’t need a large amount of it to seal the sump joints. I just need the tube to be able to fit into the chamber and be manipulated. I’m still curious, though, and intend to ask other knowledgeable people who build tanks to hear their thoughts, experiences, and advice. I’m building a foam based background with embedded river rock. I bought some clear GE Silicone I Door & Window for ~$5.55 at Home Depot. It releases Acetic acid while curing and there is no indication of mold or mildew resistant additives. I’m contemplating using it to seal the background to the tank walls and floor and hold it in place.
I was able to confirm with a number of trustworthy sources that the GE 100% Silicone I Door & Window product was perfectly fine for use below the water line in the aquarium. Again, it is a sealant and not a true adhesive, so do not use it for bonding your own custom aquarium glass joints. It may not be able to withstand the pressure and over time it could leak. I used the GE Silicone I product to seal my custom rock background to the back wall of the BioCube 14. It took just over a day to fully cure. It has bonded really well and looks excellent.
I’ve since put the rest of the tank together with organic dirt as a base substrate and Eco-complete to cap it. I’ve added my plants and driftwood and cycled the tank water for about a week. I used a couple gallons of water from my existing tank so I had established water. The rest of the tank was filled with re-mineralized RO water with Seachem Prime and API Aquarium Salt. I also used a starter bacteria to help establish the bacteria colony in the filter media. I changed 2 gallons of water every other day for the first week and the tank quickly came into balance. After the first week and the water tests showed no ammonia and the pH, temperature, KH, GH, and TDS were at normal levels, I acclimated my 2 Cherry Barbs and a school of 11 Neon Tetras to the new water and successfully moved them over.
Everything seems to be going really well, so far. The fish seem happy and healthy and are getting adjusted and comfortable with their new home. They are eating well and the plants seem to be showing signs of growth. So, all of this is proof enough for me that this particular GE Silicone is safe to use and effective and is about 1/3rd the cost relatively compared to the DAP Aquarium Sealant that is sold in a 2.8oz tube.
While the integrated 3 chamber sump in the BioCube is a fantastic feature, it has a basic shortcoming. The ability to do 3 stage filtration in the proper order (mechanical, biological, and chemical) is not really feasible without doing some modifications to it otherwise you will be creating a big mess anytime you need to change or recharge the chemical filter media because you would have to physically remove all of the bio-balls for access underneath. I don’t believe that handling and disturbing the bio-balls is the best idea. It can potentially destroy the colony of de-nitrifying bacteria or at least significantly damage it and diminish its effectiveness. By default, the BioCube uses a filter cartridge in the 1st sump chamber that has a floss trap cover with carbon enclosed. It is an okay option but I really don’t want to have to continue to buy custom $3.50-$4 cartridges for every filter change. It is a more costly choice than just using floss/fiber pads and you end up having to replace the cartridge with the carbon included every time the pad is too dirty. I’m also not really sold on carbon being used in a planted tank for chemical filtration. It will trap too much of the organic waste that is healthy for the plants to consume.
So, I found a custom media basket option for the BioCube 14, made by inTank LLC, that is placed into the 2nd chamber to allow for 3 stage filtration and makes it simple for maintenance and cleanup. I can place my filter floss in the top compartment, the bio-balls in the middle compartment and some in the lower compartment for added volume, and a Purigen media bag underneath the bio-balls in the lower compartment. It is all neatly contained so that it is easy to remove as a unit without making a complete mess. I can easily replace the floss media in the top compartment or I can pull it out and replace the chemical filter media without having to handle and disturb the bio-balls. The media basket is made out of laser cut acrylic and has a removable side panel for access to the media. you can just lay the basket sideways and remove the cover, change the media and replace the cover and slide it back into place. There is a top water director piece that sits over the top of the BioCube’s sump chamber wall between chamber one and two. This piece guides the water into the drain holes to enter the media basket. This requires a little permanent modification to the BioCube’s plastic sump wall by cutting the plastic to get the water director piece to fit and provide better water flow with a wider opening. Each compartment has different sized offset holes to drain the water from one stage to the next and provide a little more agitation to the water.
Refugium and Other Components
Using this media basket in the second chamber frees up the first sump chamber so you can use it to hide a heater, UV filter, temperature probe, aerator, or in the case of a saltwater tank a protein skimmer. You can also use one of the media basket compartments as a tiny refugium or “fuge” for plants or macro-algaes. The rear wall is glass allowing you to provide reverse lighting at night. Coralife sells a light that attaches to the back wall for this exact purpose. If you decide to reverse light the refugium, you should install the Fish Saver Guard from inTank to block the light in the sump from entering the main tank at night.
The BioCube includes a nozzle for the inlet to the tank from the pump. The nozzle is adjustable to approximately 30 degrees of center either way and can rotate 360 degrees in any direction. If you are okay with fixed water flow direction or don’t mind sticking your hand in the tank every once in a while and changing direction this should work okay. If you are looking for a little better water surface agitation and plant/coral movement and a somewhat random current for the fish, you can add a Hydor FLO Deflector in place of the included nozzle. This device uses the movement of the water from the pump to drive a little propeller/turbine which in turn cranks a little gear system that moves the deflector shield around and continuously changes the direction of the water. This is really good for oxygenation and plant growth and will provide regular surface agitation for oxygen exchange and regular currents across the plants and help to minimize any dead spots in the water. I found it at Drs Foster & Smith for $8.99 and in my opinion a very worthwhile add-on to any nanocube setup. For comparison, my local fish store wanted $21.99 for it plus tax.
The BioCube series of tanks from CoraLife are quite versatile and offer a lot of high-end features and capability with the 3 chamber overflow sump, advanced lighting and cooling, and the powerhead pump with high-capacity water movement. It will most definitely allow you to run a really healthy freshwater or saltwater setup. I’m very happy with it so far and I’m only in the process of setting it up.
I’m in the process of building a custom river rock background to cover the plain black wall hiding the sump. So, it will be 2 or 3 weeks before I’m at the point where I’m ready to put fish into it. Look for a follow-up post here covering my background build project and eventually my final BioCube setup when I get it all aquascaped, planted, and my fish transferred.