No, filters only been working for a few days, I'm assuming it's some dead plant matter...or someones been peeing in my RO water!
Or could be from your RO water. You must always always dechlorinate\de-ammonia\test your RO water as RO units are not 100% guaranteed to remove chlorine/chloramine.
Your excessive ammonia levels could be coming from your RO water.
Chlorine\ammonia in RO water can be removed by either something like Prime, or aerating/standing for 24hours before use. A test kit will give an accurate answer (free chlorine test kit and/or ammonia test kit) as there will be only one ion present, unlike fish tank water and test kits.
The chlorine in RO water comes from not using or using an exhausted RO or finally running flow too fast with a carbon/chlorguard pre-filter. The pre-filter fails to remove the chlorine, which then damages the RO membrane and passes through into the RO water. So you need a top notch, preferable Chlorguard based RO pre-filter, running sufficiently slow to guarantee chlorine removal.
The ammonia in RO water, is similar due to poor pre-filter, and presence of chloramine in the incoming water. If the pre-filter is poor (or incorrect type) the chloramine is broken down by the pre-filter to chlorine and ammonia, the chlorine is absorbed, but ammonia needs longer to be absorbed, but if left in water, passes through the RO membrane into the RO water.
The marine big boys with expensive fish, either ensure their pre-filters are top notch, have lots of pre-filters, test the RO water or just add Prime before use.