Hi

I have had my Fluval U3 running for a couple of weeks now & noticed the instructions suggest I should change the carbon/poly pads alternatively every 3 weeks or so.

Having researched this on the intranet, there appears to be a common view that these 'Carbon' pads add little value (unless you are clearing up unwanted medication).

My questions are
* Is it true that these add little value (there are carbon pads in 2 of the 3 media cartridges) ?
* What should I replace these with ?
* Will replacing these damage the build up of bacteria to any great effect ?

I probably should just say that I transferred existing media from my old filter to automatically cycle the tank (Fluval Roma 125) which currently houses 7 small communcity fish & ammonia & nitrite levels are currently 0.

Would really appreciate any advise before I go out & but replacement pads

It is true that carbon is used for the chemical filtration (eg mopping up medicine).
Replace these with filter sponge. These do not need replacing until they are falling apart (this takes ages).
The majority of the bacteria will be in the sponges not in the carbon (as far as I know).
What do you have in the Fluval Roma 125's filter?

Thanks - I have foam pads in the same cartridges as the poly/carbon. Not sure whether additional fluval foam pads with fit in there as well, or whether I will have to buy different sponge pads

Biomax ceramic rings are in the middle cartridge, which I believe I shouldnt replace.

My plants don't seem to be doing very well - might this be a result of using these carbon pads in my filter ?

It's not likely to be that unless you are dosing with liquid plant fertiliser. Carbon can remove some of the components in that. Though if the plants have recently been moved, it's quite common for them to look a bit sorry for themselves for a while until they've established themselves again.

yes I have been applying plant liquid feed to acquarium - under advise from my LFS. Currently have lights on for c10 hours per day, anything else I can do to help with their growth ?

I have the same filter in one of my tanks, the reason why Fluval to you to replace them at various intervals is simple they want your money,I've took them out and replaced them with sponge pads and not the generic type just a simple sponge block bought from my LFS and cut to size, if you really want something to polish your water look into a product by Seachem called Purigen it does work just cut one of your sponge pads in half and replace it with the Purigen.
As for your plants if you don't want a Co2 system give dosing with a liquid carbon product a go along with a good aquatic fertilizer, I would suggest maybe EasyCarbo along with TPN.

Purigen is very good, but anyone considering using it should bear in mind that it must not be used in tanks where certain types of water conditioner or slime coat promoter are used. If they contain amines (many do), these bind to the Purigen resin, and if any chlorine comes into contact they convert it to chloramine which is highly toxic. They also render Purigen useless and make it impossible to successfully recharge it.

Interesting never knew about that, I only ever use Seachem Prime as a de chlorinator so as its made by the same company I,m presuming it safe to use alongside the Purigen.

Yes Prime is absolutely fine and if you ever felt the need for a slime coat promoter, Seachem StressGuard is OK too.