Canadian tire TDS meter

[mike31154]

I ran canister filter for months with and without GFO (along with carbon) and couldn't tell the difference on my Hagen phosphate test kit. Maybe it's 'cause it's hard to read. The test result is never anything like the colour chart. Almost clear so I can only assume negligible to zero nitrates.... with or without GFO. Stopped running the GFO a month or so ago and no appreciable difference in algae growth. Still run carbon. My Chaeto grows well either way. So from my own experience, running GFO appears to have been an expensive proposition with no discernible benefit.