Never thought about that...I definitely have the room to do so.
My original question was whether or not carbon would strip out the excess lanthanum in the water..The reason I ask is I did an ICP after I did my first dose of phosRx and I had a small amount of it show up in the test. Wasn't enough to raise any concern, but I wonder if it will harm things in the long run if I don't skim it out (and was hoping to use carbon as a way of pulling it out of the water).
I'm not sure if its the particulate that's harmful or the lanthanum in the water that I need to worry about
Lanthanum precipitate as LaPO4 is not neccessarily harmful, but you'd prefer to be able to export it out of your tank if you can. The easiest way to do this is by physical means such as filtration through a sock or a reactor with a filter on it (which is how I did this many years ago. My PO4 was >6 IIRC and my rocks were a huge sink). Activated carbon will most likely not adsorb it. However, Free Lanthanum as LaCl3 might be adsorbed as La+. Off hand, I know that activated carbon can adsorb heavy metals depending on how the carbon was activated. And, Lanthanum is on the bubble in terms of being a heavy metal.
Bottom line is to drip/dose really, really slow and measure regularly. But, having said all that, IMO, your phosphates aren't high enough to go to all the trouble of using lanthanum.