Kyle
You will see some past articles on GAC where they want you to change GAC ever week or less. If you look at dye adsorption cures, the adsorption rate takes a big dive in the first 24 hrs or so. If you let any of these go to long, ~ 1 month, they go biological and loose their effect. I have also been working with Ken Feldman on GAC and his data also shows about 1/m on GAC. I have also talked to GAC tech that keep tanks and they also concur 1/ m. You have to remember these are all pours media and molecules will plug them up in time, as they are also acting as a mechanical filters. If you want to go with Purigen 1/ 3 m fine but IMHO that is way to long. Purigen is different than GAC, as there are no tests on it and no adsorption rates to go by like GAC.
Matrix. I like it in a reactor for 3 reason. It has better fluid dynamic properties, as it is round and there will be less channeling and chimney effect. It has good data numbers. And lastly is also hard. However, if you looked at the price list I gave it is not worth it, as it is way more cost wise than ROX and has a lower adoption rate than ROX. Its better fluid Dynamics will not make up for that. I never worked out the cost of Matrix until a guy PM me about it and was floored at the cost. Also, Matrix is more user friendly. Many have complained about using ROX in reactors. Most just solve this by using a mess screen so the ROX needles can not get through.
rs1831 and Kyle
I have no clue why BRS has it set up that way they do but it is *** backwards. Why ? GAC is most both a chemical and mechanical sieve. It is the GAC that will do most of the filtering over GFO or Purigen in removing particulate and large molecules, as the pores are larger. So, ask yourselves the question, why on earth would one want to plug up the Purigen or GFO first, especially the GFO, which is suppose to be removing PO4, not particles or large organic molecules. You will kill that GFO's pore and surface area rather quickly.
Water should flow through GAC---> Purigen---> GFO
Lets put this in more Dick & Jane terms. You want to filter some water using screens.
BRS says
Water-->1 in Screen --> 2 inch screen --> 3 inch screen
Now, does that make any sense to you
I say
Water-->3 in Screen --> 2 inch screen --> 1 inch screen
Now, doesn't that make much more common sense ?
Your GFO and Purigen also cost more than GAC, so why kill them first ?? They are also more selective, so again, why kill them first.
It is best to keep all 3 separate if one can. However, it is also best to put some granular media in with the GFO, such as a spoon full of GAC mixed with it. This greatly helps stop the GFO from clumping and turning hard as the GFO needs some void space and it lasts a little longer this way.
Some also like to mix these. If that is ones cup of tea fine but it is not the way it should be done for max efficiency for of any of them, as their adsorption rates are not the same. Andy filtration expert will tell you not to mix different mess media or adsorption rate media together, as it is self defeating.
Doing that once a month is a lot of work
That is not much work at all and is what most do and some do it every two weeks and even some every week, as the adsorption rates of fresh media are so much better.