Restarting cycle after killing cyanobacteria

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lectraplayer

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Feb 17, 2014
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After using erythromycin phosphate for a week to kill cyanobacteria, I'm trying to get my cycle started again. I have plants in this tank which are diggin' and reachin' better than expected. I've dosed an ammonium nitrate fert and p to give me a total of 2PPM ammonia. The last two or three weeks, the ammonia has just sat without me adding anything farther. Again, the plants are loving it. No fish. Can ammonium nitrate not be broken into nitrite->nitrate?

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Why do you need to recycle the tank since Erythromycin doesn't kill or harm BB. What happens when it's used for 5 days to kill cyano is you often get an ammonia spike due to cyano die off which continues even after your done dosing. Water changes bring the ammonia down and if you don't want to do a WC or can't then your BB will increase in a mini cycle.
 
Ok. I keep seeing that Erythromycin WILL kill nitrifying bacteria, and the cycle I had before has completely halted for the past two weeks. Any idea why my nitrites and nitrates are staying down since I have the ammonia for them to process and they "should" still be present and active?

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What is your ph? When ph drops below 6.5 biological activity slows. When it drops to 6 or below biological activity stops and BB can begin to slowly die. When this happens you will see ammonia but at low ph ammonia isn't very toxic to fish. If ammonia is present in a low ph tank that means the BB can't process it so you won't have the biological activity to convert the ammonia to nitrites or nitrates.
 
With a Ph of 7 and a temp boosted to 85・F

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I've used it in tanks for over 30 years and never had an issue with BB. Did you only use it the 5 days as directed? Have you done any WC's since dosing the tank? Cyano continues to die off after treatment which will cause ammonia and the more die off you have the more ammonia. If there is more ammonia in the tank that there is nitrosomonas to convert it into nitrites then the tank will have a mini cycle.
 
I did use it per directions, though my package didn't say finish with WC. Did a 90% WC yesterday morning and saw a good sign last night-water was clouded opaque. Shouldn't I keep seeing nitrates coming during a mini cycle? I was not.

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It depends if you have plants, what kind and how many since they will use ammonia before it can convert to nitrates which they also use. For right now personally I'd give the tank time to settle and do water changes as needed to keep ammonia no higher than .25ppm. Plus after a 90% WC you may not see nitrates for some time especially if you do large weekly WC's. What does the tank normally run at on nitrates? All my tanks run at 10ppm or less on nitrates and a couple tanks with only nano fish and a lot of plants tends not to show any nitrates unless I add them.
 
I can support River in the fact that I have a planted tank and getting the nitrates above 5, even after two weeks of no water changes, is proving difficult. And I rarely see ammonia or nitrite.
 
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