Where Is The Ammonia Spike?

[Curiosity101]

With such a tiny bioload in such a big tank in the beginning then a fish-in cycle can be done fine as you've seen. But the thing is when people do a fish-in cycle they often do it by accident (on advice from a lfs). For example for a 60l tank I've often seen around 6 Danios recommended to cycle it.
This is the equivalent to you starting your cycle with about 28 guppies...see the difference? lol.

Onto the nitrate sponge question, I reckon you should take it out. If you have an established bacteria colony (and with there being so many sponges already in it). Then you shouldn't see much of a spike, IF you see a spike at all.

 

[roadmaster]

With such a tiny bioload in such a big tank in the beginning then a fish-in cycle can be done fine as you've seen. But the thing is when people do a fish-in cycle they often do it by accident (on advice from a lfs). For example for a 60l tank I've often seen around 6 Danios recommended to cycle it.
This is the equivalent to you starting your cycle with about 28 guppies...see the difference? lol.

Onto the nitrate sponge question, I reckon you should take it out. If you have an established bacteria colony (and with there being so many sponges already in it). Then you shouldn't see much of a spike, IF you see a spike at all.

+one. Would not believe this particular expierience to be rare, so much as Lucky. Could just as easily have been quite a frustrating expierience for the hobbyist, and a deadly one for the fishes.

 

[waterdrop]

Yes, agree with C101 and the others, this could easily have been a silent cycle case, given the large tank and small number of fish, added at intervals. Agree that he water change habit should be moved to weekly and testing should continue at least at those weekly maintenance times just in case the bioload eventually produces ammonia and/or nitrite that reveals the biofiter to not yet be adequate. My suspicion is that its cycled though.

~~waterdrop~~

 

[guppylad]

Thanks! Happy to take the nitrate sponge out - though could you give me a little more info on exactly why it's best to do this - just so I have a better understanding of the processes involved and what's happening in my tank?

 

[Curiosity101]

Just because it will hopefully proove one way or another if your tank is cycled.

The end product of the cycle is Nitrates, you said your tank is only showing trace amounts. If the sponge is doing it's job and removing what little nitrates are being created then you wont know for certain your tank is cycled until you remove it.

So remove it and leave the tank for a few days, don't do any water changes as this could either dilute or introduces nitrates (depending on your tap water reading of nitrates). And see if the nitrate levels have increased at all. If they have they you're cycled

Just one note though, I definitely agree with others that have suggested you up your water changes to weekly.

 

[OldMan47]

Your 75 gallon tank with a small number of guppies and decent water changes every 10 days could well cycle without giving any adverse chemistry readings. I would stop adding fish for a while and just wait a few weeks. If you are cycling without getting high enough readings to notice, that will give the bacteria a chance to catch up before you add any more fish. I have cycled many large tanks in my life in much the same way as you are doing by putting a light biological load into a large tank and just waiting. With the small bioload, the levels never do get very high before the bacteria start to control them.