Marine Biotech X-Rack System


Advantages and Disadvantages




The Marine Biotech X-Rack system is designed to house frogs. It is a flow through system using re-circulating water. The system contains mechanical pre-filter pads, cartridge particle filters, charcoal filters, biological nitrifying filters, and two UV sterilizing lamps. The water is pumped into piping that takes it to the tanks (Fig 1). Wastewater and debris empty from the tanks and are collected through a series of gutters. Water coming from the gutters is first channeled to a pre-filter pad, which traps most of the large waste and particulates (Fig 2). In the Marine Biotech system, the pad is quite large and functions well. There are two layers of padding, a coarse top layer and a finer lower layer. These pads need daily cleaning.


The water passes through the filter pad into the reservoir, where it is exposed to the biological nitrifying filters (Fig 3). The bacteria growing here are critical for removing toxins and wastes and improving the quality of the water. The reservoir contains a pump, which constantly circulates the plastic pellets containing the bacteria, supplying them with oxygen they need to function. In addition, there is a temperature probe and heater in the reservoir.


From the reservoir, the water is pumped to the filtration and purification system. This includes a series of cartridge particle filters, which look very much like swimming pool filters (Fig 4). These cartridges trap smaller debris not collected by the filter pad. The canisters housing the filter cartridges also contain carbon socks, which remove chloramines and other potential toxins.


The water then passes through two UV lamps for sterilization of biological contaminants (Fig 4). Water is next pumped back to the tanks. Between the dripping water and the water pump, the room can be quite noisy. We have found the pump to be much quieter than others we have used, however.


In most recirculating systems, water is typically obtained from the municipal source and is then treated either by a reverse osmosis system (R/O) or by a series of charcoal filtration units. RO systems remove nearly everything from the water and therefore salts have to be added back either manually or automatically. This treated water is then stored in an external water reservoir. Often this can be stored in the frog room where the water can then equilibrate to the ambient (warmer) temperature of the frog room or a heater can be added to heat the water.


Our system does not have an external water reservoir. We chose not to get one because of cost. Water is instead added directly to the system reservoir from a hose supplying dechloraminated (charcoal filtered) City water (Fig 3). An overflow pipe in the reservoir under the tanks allows a constant partial water change, adjustable to any rate of flow from a small trickle to a large flow. We keep the overflow at about 20% of the system volume per day, and increase it if we need to lower ammonia levels. The recommended overflow is 10%, but we are unable to regulate the flow from our water source at this low rate of flow.




Fig 1: Piping supplying water to each shelf. Each rack has a flowmeter, pictured at the center.

Fig. 2: Pre-filter pad collects large debris from the waste collection system before water enters the reservoir. We like this pad because it is large, and the drainpipes are removable for easy cleaning. The pad is removed and hosed off daily.

Fig 3: Water reservoir, with hose supplying dechloraminated water. Overflow pipe is visible at back right.

Fig. 4: Water pump shown at lower right. Two UV bulbs at top left. Three mechanical filter canisters are in the middle. We currently use two filters.

Fig 5: Racks of one liter tanks allow for compact storage of many frogs.

Fig 6: Racks of larger 4 and 6 liter tanks for housing groups of frogs.


Monitoring Equipment


Our system does not have all the monitoring and control equipment that Marine Biotech has available. We have an alarm system to alert us if the reservoir water level drops too low, as well as a temperature control unit with an alarm. We find this unit invaluable in regulating water temperature, since there is no reservoir in which the water temperature can equilibrate before entering the system. Refer to the Marine Biotech website for other available equipment and features.


Racks and Tanks


We have two racks (Marine Biotech XR-6) with seven shelves each, which hold 196 1 liter tanks (Fig 7). We house two frogs in each tank, allowing us to keep a large number of frogs quite efficiently. The shelves for the 1 liter tanks do not have water tubes which fit into the tanks, but rather small nozzles in the water pipe from which a stream of water flows into the tank (Fig 8). Care must be taken to ensure the tank is properly placed under the stream.


We also have 2 racks with 5 shelves each, holding 4 and 6 liter tanks (Marine Biotech XR-1) (Fig 6). We house groups of frogs in these tanks, at a density of 1 – 2 frogs/ liter. These tanks are relatively shallow, which suits X. tropicalis. There is good headspace, preventing the frogs from jumping out. The lid has a large feeding hole. There is no method to snap the lid securely, which is a concern, but has not been a problem so far.



Fig 7: Back view of small tank. The opening must be sprayed out 1 – 2 times/week to prevent clogging. Also ensure the drain plug is securely inserted in opening. We have found the plugs tend to loosen and fall out over time.

Fig 8: Buildup of debris in the tray holding the small tanks. We remove tanks weekly and wipe down the tray, as the debris is not adequately removed by water flow. Water jet can be seen flowing into holes in lids.

Fig 9: Six liter tank with lid removed to show drain. Several types of drains are available. This is a mesh filter, which works well. It must be changed out or cleaned weekly, and checked daily for clogs. The inside of the black bulkhead fitting is flushed out with a strong spray of water when the drain is removed.

Fig 10: Food tends to collect around the feeding holes of the 1 liter tanks. Use of a funnel or daily cleaning is necessary.

Fig 11: We find a squirt gun invaluable for clearing drains, cleaning gutters etc.

Fig 12: Modified drain supplied by the company removes debris better, but can only be used for larger frogs.




We have found the system relatively easy to maintain. We have had to make few modifications to the tanks and other parts of the system for it to meet our needs. While the Marine Biotech system is quite expensive, the time savings in labor makes up for initial cost.


Daily maintenance includes water quality monitoring, checking various system functions, checking/adjusting the water flow to each tank, and checking tank water levels for possible drain blockage. The double-layered prefilter pad is also cleaned daily. It is very large and functions well to trap the majority of gross debris.


Weekly maintenance includes removing the drain filters in the four and six liter tanks to check for clogs, and cleaning tanks and gutters. The small nozzles supplying water to the 1 liter tanks tend to clog with debris. These need to be cleared weekly. A large size paper clip works well for this. We find the cartridge filter needs changing about once a month. Between changing, we remove the cartridges and thoroughly rinse them with a strong jet of water. The cartridges can also be soaked in a 10% bleach solution to dissolve organic matter and extend the life of the cartridge. We change the carbon pellets about every 2 weeks. The quartz sleeve for the UV units is cleaned every other month, and replaced every 9 – 12 months. The bulbs are easy to monitor and change. A complete maintenance checklist is supplied with the unit.





The main problem we have had is with the shelves for the small tanks. The debris exiting the tanks tends to collect in the tray around the tanks, instead of being flushed out of the drain located at the end of the tray. (Fig 8) The shelf drain itself is also quite small. We remove all the tanks from the shelf weekly and manually sweep the debris out the drain. The main issue here is the potential for the tanks to be mixed up when they are replaced. Regardless, each tank is labeled with frog ID numbers, and we are actively putting identification tags in the frogs themselves. However, mixing up the tanks can make it more complicated to find the tank where a frog is supposed to be.


The small tanks tend to collect food debris around the feeding hole (Fig 10), which quickly molds. Food must be washed off daily, or a funnel should be used.


We have had a problem with tank drains getting clogged with debris (Figs 7, 9, 11). If the drains clog completely, the tanks will fill with water and the frogs can drown. We change out the plastic drains on the larger tanks and flush the drains with a strong jet of water weekly (Fig 11) to prevent clogging. Marine Biotech has supplied new PVC drains (T-Skimmers) for the 6 liter tanks, which we like (Fig 12). These large bore PVC pipes extend from the bulkhead down to the bottom of the tank. They effectively suction up large amounts of debris, and tend to clog less due to their large diameter. The only drawback is smaller froglets could be sucked up the pipe. We use these drains for larger adult frogs only.


We have found the Marine Biotech company to be very responsive to our comments and problems, which is important when dealing with a complex system such as this. They have suggested methods to alleviate some problems, and are working on methods to solve others.


Following is a summary of the advantages and disadvantages we have found with the system.