Semi Automatic Operation of an NFP Nitrate Reactor | D-D The Aquarium Solution

The NFP reactors can either be operated manually, semi automatically or fully automatically.


This will depend on the application and level of sophistication that you want to go to. The first part of these instructions describes the operation of the unit without the need for any supplementary equipment other than a reliable high sensitivity nitrate test kit which is not supplied with the unit.


For those people who do not want to inject the unit on a daily basis

If you want to have a semi automatic method of operating the filter without going to full automation then there are two possible methods.

1 – Use of

Deltec Osmotic Nitrate Bags.

2 – Use of a peristaltic pump to supply the Nitrate fluid.


These special bags operate using the principle of osmosis through a semi permeable membrane. The bags are refillable and hold 250ml of Nitrate Fluid which they release slowly over 4 -5 weeks through the bag walls which are made of a semi permeable membrane material. This gradual release supplies the bacteria with food continuously without any further requirements for daily injections.

The Nitrate bags fit into the reactor body in the space above the bacterial media. The number of bags that are required will depend on the size of the reactor and the size of the system on which it is being used.

A single bag will release about 50ml of Nitrate Fluid per week or 7ml per day which makes it ideal for the NFP509. Two bags will release 14ml per day; 3 bags – 21ml and so on.

Use of the Nitrate Bags

Each membrane bag is fitted with a bung which is removable for filling with the Nitrate Fluid. Fill the bag with 250ml of fluid, replace the bung and place the bag within the reactor body in the space above the bacterial media. Refit the lid of the reactor.

If you are using more than 1 bag then remember to mark each bag so that you know when each needs to be refilled.

Follow steps 1-10 as shown in the manual instructions.

From step 6 onwards it is obviously not necessary to use the injection system any longer as the semi-permeable bags will carry out the function of feeding the Nitrate Fluid to the bacteria.

There is normally sufficient Nitrate Fluid in the system to last for 5 weeks however we recommend that you empty and refill the bags after 4 weeks to ensure that the bacteria do not run out of food.

Obviously with this method the reactor is supplied with food at a constant rate which can not be varied other than by adding an additional bag. As the feeding rate will determine the amount of bacteria in the system and therefore the final water flow through the reactor then this method will not allow the reactor to reach its maximum possible capacity.

Note that at the end of the 4 weeks that the bag will still be full of water as only the alcohol is allowed to pass through the membrane and into the reactor. Empty this water away and refill the bag with fresh solution.

To refill the bag, first switch off the recirculation pump and nip the water supply by folding over the feed pipe or switching off the feed pump. Remove the Nitrate Bag, empty and replace its contents then return it full to the reactor. Take this opportunity to clean the build up of bacteria from the outlet pipe and lid.

When you are changing over the bag it is important to ensure that you do not waste too much reactor water during the change over as this will need to be replaced with fresh tank water which will have a higher redox. After refitting the lid, allowing it to refill and then switching on the recirculation pump we would recommend that you turn feed water supply back off for a couple of hours to allow the redox to fall again allowing for the replaced water.


As with the Nitrate Bags, this method automates the feeding process but does not control the redox or water flow rate and is an intermediate step towards full automation of the system.

For this method you will require a dosing pump with a flow rate that is suitable for the amount of food that you are required to add on a daily basis. You will also require a digital plug timer that it is possible to control down to second intervals.

Connect the peristaltic pump to the non return valve as shown on the fully-automatic diagram. Note that some cheaper pumps do not automatically seal when the pump switches off and therefore if the pump is mounted above the reactor it can allow siphoning of the food into the reactor even if it is switched off. Always use the non return valve or the water can back siphon.

Always read the operating instructions for the pump that you chose for the task.

If your reactor requires 8ml of food per day then we would recommend that you feed it as 2 doses of 4ml or ideally 4 doses of 2ml per day; the ability to do this will depend on the volume capacity of your peristaltic pump. As the feeding requirement increases then simply increase the duration each day that the pump is set to dose the reactor with Nitrate Fluid.

Follow steps 1-10 as shown in the manual instructions.

From step 6 onwards it is obviously not necessary to use the injection system any longer as the peristaltic pump will replace this function and will carry out the feeding of the Nitrate Fluid to the bacteria.


6 - Shut off the water supply to the reactor using tap ‘Y' and leave it like this for 3 days to allow the oxygen in the water to be used up and to allow growth of the anaerobic bacteria.

Feeding the system: The bacteria within the reactor must be supplied with a carbon based food, (Deltec Nitrate Fluid), on a daily basis throughout the duration of the reactor's use. To make this possible when using the manual method, Deltec supply you with a plastic syringe ‘X' which should be first filled with Deltec Nitrate Fluid and then fitted to the end of the non return valve at the inlet to the recirculation pump.

The amount of Nitrate Fluid to add to the reactor will depend on a number of factors such as the flow rate and the level of nitrate in the water. When first starting the system we recommend that 4ml of Nitrate Fluid should be added for each litre of biological media within the reaction chamber over a period of 24 hours, (detailed in table).

For the purpose of these instructions we will use the NFP509 which has a reactor media volume of approximately 2lt.

On days 1 - 3 whilst the water flow rate is switched off it is necessary to add 8ml of Nitrate each day. This should be added in 2 doses of 4 ml, one in the morning and one in the evening.

7 - On day 4 open up the tap ‘Y' very carefully until you achieve 1 drip every 3 seconds and wait for a further day before testing the outlet water. Continue to feed the unit morning and evening with the same volume of Nitrate Fluid as was used for the first 3 days.

8 - Day 5 - check the water coming out of the reactor at ‘Z' for nitrate level using a reliable nitrate test kit. If the reading from the water is zero then increase the flow rate by no more than 1/3 of its current rate to one drip every 2 seconds and wait for   2-3 days for the level to drop back to zero. Continue to feed everyday with the starting volume of Nitrate Fluid.

If the reading still shows that there is nitrate coming from the reactor then wait another day and another day until you achieve a zero reading before increasing the flow rate. Continue to feed the unit morning and evening as on the first 3 days and wait until the reading drops to zero.

Initially, whilst there is still oxygen present at sufficient levels within the reactor, aerobic bacteria may grow within the media converting any ammonia in the water to nitrite or nitrate. This may show as a slightly elevated nitrate or nitrite level coming out of the reactor compared with that of the water going in.

Note: Large incremental jumps in flow rate especially at this stage can crash the growing bacterial culture within the reactor by the introduction of too much oxygen which will raise the redox and will slow down the maturation period.

9 - Gradually, in stages which will take 2-6 days between changes, it should be possible to slowly increase the drip rate from the reactor by 20-30% at each step, then to wait for the reading to come down to zero before increasing the flow again. The ultimate goal is to turn the volume of water in the tank through the reactor once every 14 days as a maximum and once every 28 days as a minimum. At this flow rate it will be possible to keep the nitrate levels fully under control.

Increasing the amount of food: As you increase the water flow rate through the reactor it will also be necessary to gradually increase the amount of food that is dosed every day. This is the tricky part and it will require a little trial and error by the user to learn how much extra to add as you increase the flow rate.

By the time the reactor is running at maximum capacity it will be necessary to be adding about 25% more food than was being added during the initial stages which for the example for the NFP509 means up to 11ml per day. If due to the size or your tank relative to the reactor you do not need to achieve maximum capacity then it is possible to just continue at the initial feed rate.

Be careful not to overdo the additions of the food as this will tend to reduce the redox to below 200 and can often be seen as cloudiness in the tank.

If not enough food is added you will find that it will not be possible to increase the flow rate further as there will be insufficient food to support a large enough bacterial colony to achieve a zero nitrate reading for the set flow.

10 - Once the system is running in a stable manner at a flow rate which gives you sufficient volume from the reactor to turn the volume of the tank over every 14-28 days then continue to feed morning and night at that set volume to maintain the nitrate level in the system.

See the paragraph at the end of the section on fully automatic operation on what to do when the level of nitrate in your system gets down to zero.