Is my tank almost finished cycling

[Salutationsb]

setup for about 4-5 weeks, initials params were 0 ammonia, 0 nitrates, 0 nitrates. Now Im getting 0.25 ammonia, 15-18 nitrates, 0 nitrites. I am finally on the verge of the cycle ending??

I have a AC 70 and AC110 running on a 75 gal tank.

temp at 78-80 with a fairly stable ph of 7.6

Inhabitants are 2 sevs (6in, 2in) 2 geos 4.5in, 1 Uaru 4in, 1 pbass 7in (he is being re-homed shortly).

Any help would be appreciated, should I do water change or will that further delay the cycle.

 

[TwistedPenguin]

Ammonia should always be zero but with your nitrate reading it would indicate some sort of a mini-cycle. Such as when you accidently dump too much food in or a fish dies & starts rotting before you notice it, etc.
You're definitely already cycled with a nitrate reading of 15-18 ppm. I would most certainly do a 50-60% water change at this point. That would do away with the slight ammonia reading plus drop your nitrates back down to 9 ppm or so. I like to keep my nitrates below 10 ppm, although most people keep them between 20-40 ppm.

 

[HarlanAshmore]

lookin ok but there shouldnt be any ammonia

 

[hybridtheoryd16]

A normal fishy cycle can take up to 8 weeks.

And usually goes like this---you start to get a ammonia reading and then after you have had a ammonia reading for a while you start to get a nitrite reading. This tells you that the first part of your bio bacteria is colonizing and consuming the ammonia and turning it into nitrite.

As your nitrite reading climbs higher you should notice the ammonia reading start to fall and eventually go to zero. This tells you the first part of the bacteria is become more populated to the point to where it can handle the bio load and consume all the ammonia. Also shortly after you see a nitrite reading you will start to see your nitrate reading climb slowly.

After the nitrite has risen and the ammonia level has fallen to zero, the nitrite will then start to become colonized to the point where it can handle the bio load of the system. And slowly the nitrite reading will fall to zero as well. The entire time the nitrite reading is falling the nitrate reading will be climbing.

So in short if you have went thru a ammonia rise and fall and a nitrite rise and fall. Then yes you are getting close to completing the cycle for the given bio load.

I would do a water change when at any time you get a ammonia or nitrite reading of .5ppm or more.

You will start to get nitrates well before the cycle has completed. The only worry I see is that you have zero nitrite. With ammonia present you should have some nitrite as well. Because the ammonia consuming bacteria always colonizes completely before the nitrite consuming bacteria.