Hey Chris,
We can tweek your sump to perform better in the long term and id suggest doing it now before you go to far down the track.
Get others opinions first and do your own research but ill try and explain a bit of method behind the madness. I know ill be recapping a lot of stuff you probably already know but thought id try and paint a fuller picture for others that may read on later.
The filter wool and sponges are great for removing debris from the water but gather debris and end up causing nitrate issues. The reason reason for this is debris is trapped there and bacteria will begin to break it down but they cannot complete the cycle of completely breaking it down because their density does not allow for suboxic conditions. There is a little more to the nitrogen cycle that usually explained, here is a diagram showing the current belief on its stages.
[Broken External Image]:
http://www.advancedaquarist.com/2011/4/chemistry_album/Fig_1.jpg
So in an oxic (oxygen present) environment you will never go beyond the nitrate section of waste disposal through biological breakdown.
Some people use filter socks etc to achieve the removal of debris but it requires the sock to be removed every 24 to 48 hours swapped with another. The removed sock then needs to be soaked in bleach to kill the bacteria and break down the waste its collected before it can be reused. Traditionally I have always though that the work on this outweighs the benefits but am starting to come around to the thought and I may have a crack at in on my next set up.
Skimmers are the back bone of modern reefing filtration, they work by removing the waste before it has a chance to break down biologically. In your current set up waste gets passed through various biological medias before it goes to the skimmer., skimmers also like a constant water level or they go out of tune, so having them in the last chamber with an ever changing water level means that you will find it very difficult to achieve good results, its also getting last bite of the waste cherry where it is most valuable getting the first.
Matrix provides the same effect as live rock rubble in a ref tank, nothing wrong with using it instead of live rock, being in a bag makes it easier to shake off debris, keep using it cause you have it but i wouldn't be throwing any more money at it to increase the amount you have when smashed up LR does the same thing.
Looks like your using polly filter, that is fine you can use carbon and a rowphos or other ferrious oxide based medias they are great at doing what they are do. polly filter at least shows you when its past its used by date by changing colours. only think i don't like about it is that its essentially a sponge/filter wool so can trap debris, but just need make sure you use it in the last stages of the filter as you have.
So what I would suggest doing it chucking the wool/sponges in the fist two chambers, removing the glass and making them into a larger chamber, install the skimmer in this section to give it the opportunity to remove as much waste as possible before it gets a chance to break down. Place the bag of matrix under the poly filter.
You then need to have a method of managing your nitrates and phosphates. The live rock in your tank and the matrix in the sump will manage your nitrates a bit but usually not to the extent that is required once your system is in full swing.
Some people use macro algae in refugiums in reverse light cycles and this does work and has other benefits, but the design of you sump makes it difficult to incorporate to a successful level.
You then can create suboxic environments to manage your nitrates by using deep sand beds or marine pure or nice big porous pieces of LR.
Carbon dosing as you have already started to play around with can be very successful but needs to be done correctly or it will cause sever issues. It works by feeding bacteria which bind the nitrates and phosphates within themselves as biomass and you then skim the out of the water table using an over powered skimmer. It can be done with products like vodka, sugar and vinegar, bio pellets or the Red sea nophox like you already have.
Given your friends with Talbot id suggest grabbing a couple of 4" thick marine pure blocks from him (this isnt to say an ice cream bucket full of sugar fine aragonite wont do the same thing, just the if you friends with him its easily and cheaply at your disposal) and throwing one in the first chamber with the skimmer and one in the last with the return pump and using the RS nophosx but as per directions, which is constantly and adjusting the dosed amount to reflect your water parameters (no sudden changes)
So to recap, i think ditch the wools, merge the first two chambers, have your skimmer and a marinepure block in there, pop the matrix under the polly filter/carbon/ferrious oxide (whatever you end up using) and then have return and another marine pure block and keep up the carbon dosing.
You can also tell me to shove it and I like it the way it is hehe, but as I said seek others opinions before making any changes, but that is my advice/suggestions for what its worth.