Are you using the same substrate and food for both tanks? Live plants in either tank? Any rocks in the tank with high po4
? With 160 ppm
nitrate, it sounds like its been a while since you've done a water change, so I think that would be my first course of action. Atleast 50%. They day after, do another 50%, followed by another the following day. Your nitrates should be well under 20-30 ppm
by then which is much more manageable than 160 ppm
As far as a bacterial colony, as long as your tank is reading 0 ammonia and 0 nitrite, you don't have a problem there.
Also, sorry if you already mentioned this, but what does your tap water test in phosphate? How about nitrate?
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