With all nitrate filters you can not run a set flow through the media as you must provide an environment without oxygen to allow the anaerobic bacteria to remove the oxygen from the nitrate to form nitrogen gas.
This means that in the early stages you must have a very slow flow which will increase as the bacterial colony increases and can handle more water.
All denitration filters take a while to set up and you must be patient.
With a Sulphur Nitrate filter the bacteria use the sulphur as food to grow and this food is already in the reactor. As the nitrate reduces to zero it is very difficult to back off the reactor as they have plenty of food available. With an alcohol fed system you must feed it every day but then when it is matured and has done its job you can control the amount of bacteria by the amount of food and the flow rate that you use.
This allows you to balance it to match the amount of nitrate that is being produced by your tank. With sulphur systems you normally end up taking them off until the level raises again in the system.
Now the sulphur filters certainly work and are less expensive to buy however they are harder to start and have the above issues once they have done their job.
The priciples of both filters are the same so read both sets of instructions to fully understand the system.