"Pszemol" wrote in message ...
I have checked the website you linked (http://www.guayni.com/mytank.htm)
and I noticed that the measurements history does not start at January '06.
Do you have any data from before September ? Could you share them online ?
Also - please note EXTREMELY high readings for nutrients in your tank:
you show 100mg/l of nitrates and 1mg/l phosphates. Maybe this can be
tolerated by fish only tank, but it is not very healthy for fish...

One more thing - what kind of tests were used for testing nitrates
and phosphates in your tank ? What brand/manufacturer ?

For most of the aquarium grade tests, 100mg/l mark would be at the
far end of the color scale, so it is completely possible you have
there much more than a 100mg/l of nitrates. This happened to me
once in a freshwater tank full of guppies and mollies where I did
neglect water changes for about half a year. I tested the water
and got 100mg/l of nitrates, so to be sure I diluted aquarium water
sample ten-fold to get expected reading 10mg/l - I got about 20-40mg/l
instead which mean that the tank water had concentration close to 200mg/l

Maybe the same is in your tank ? Better do some water changes, soon!