What is the Peguin 70 rated for? UGF don't work real well from what i hear, but it's not your main source of filtration so thats good.
What are your ammoina and nitrite levels, if they are zero then you have enough biofiltration. If you have particulate matter problems you might not have enough flow, all your fillters add up to enough but none create a large flow. Also the power heads are sucking stuff down to the gravel (if you have the set up on the down tubes pulling from under the gravel). They make reverse flow kits for some power heads that shoot the water down the tubes forcing water up through the gravel which should help keep stuff of the gravel and able to be filtered out. With this set up you can put a sponge filter on the intake of the power head to help filter the particulate.
I would maybe start with that and if that doesn't help you could buy another power head and have it shoot twoards the gravel helping keep stuff in suppension so it can be filtered out, Koralia's work really well for this, i have one and love it.
This is all if your ammoina and nitrates are zero, if they are not zero then you need for biofiltration.
Oh yeah also how often do you do water changes and how often, when doing so using a gravel shipon to vacum the gravel whould help, also turn off the power heads when doing so if they are set up to pull from under the gravel.
Hope that helps, let me know if you have more questions.