Why such high nitrates during cycling?

[Aquavaj]

It's around the 80pp range (can never tell with these color matching tests). Ammonia and nitrite are both 0. I didn't do any water changes during the cycle but starting tonight I'm going to do 5g changes til it drops into a more acceptable range. How did it spike up so high?

 

[mcgyvr]

Totally normal and not out of the ordinary at all..
Your input simply exceeded your tanks current capacity to export it..
Which is VERY common for the first 8+ months of a tank from my experience unless starting with very well established live rock..
After about that 8 month mark maintaining low nitrate levels gets fairly easy.. But those first months can be a PITA...


Its quite easy/fast to get the "nitrifying" (converts ammonia/nitrite to nitrate) bacteria established..
It typically takes longer to establish sufficient "denitrifying" (converts nitrate to gas) bacteria..

I'm not sure the size of your tank but if its 10G then 5G is a good starting point..
If your tank is larger than 10G I'd highly suggest shooting for a 50% water change..

In general a 50% water change will reduce nitrate levels by 50%.. 20% by 20%,etc.....
So if your tank is 100G then a 5G water change is going to do VERY little for your current nitrate level..

 

[Aquavaj]

It's 40g but less than that cause it's an AIO plus all the sand and rocks too. I read that I should do small changes over a period of several days so that was what I was shooting for with the 5g/day. But I guess since there's no livestock a 50% change shouldn't shock anything.

 

[thegrun]

I would make a 100% water change, no need in fueling an algae bloom right off the start. 80 seems a little higher than what I would expect after a cycle, did you feed the tank a lot during the cycle or have a lot of die off from the live rock if you used live rock?