Nitrates - why the spike?

[pseudorand]

I have a 120gal that's about 1 month old. I started it with liverock from craig's list, as well as two large clarkii clowns a 3-stripe damel and misc inverts (all craig's list rescues). I've seen positive nitrate tests since week 1 but I've never seen ammonia or nitrite, so I believe it's fully cycled from the liverock. However, today my water test showed nitrates of 40ppm. 10 days ago it was 10ppm and had been very slowly rising since I first set up the tank. The only thing I've added since initial setup are 25 snails of various types, which were added about two weeks ago.

It's certainly not a panic situation and I realize the solution is water changes and/or other methods of nitrate export. However, I'm curious as to the acceleration of nitrate accumulation. Would anyone care to vote on and/or add to the hypothesis below:

a) Before the snails, algae was using the nitrates. But the snails made quick work of it. Now that it's gone, the combination of less algae and more bioload from the snails caused a spike.

b) The biomass that didn't make the transport of the liverock is decaying exponentially, and the bacteria population that processes it is growing exponentially, so nitrate production is exponential.

c) My two large clarkii clowns were too scared to come to dinner right away, so lots of food got wasted at first and was slowly decaying. Now they're true-to-species voracious eaters and gobble up every last bit. The fish eating the food accelerates processing (i.e. maybe bacteria process fish waste quicker than uneaten food), resulting in quicker nitrate buildup.

Those are all just guesses on my part. Do any of them fit with anyone else's experiences? Any other guesses as to why nitrates spiked?

My solution tonight was a 50% water change which reduced it to 20ppm. (I only did 50% because I mis-measured my salt and had to dilute it, so I ended up with more water than I originally planned).

 

[Retro Reefer]

It could be a lot of things but most likely it’s from the rock not processing No4 efficiently yet, what kind of rock is it? Was it wet when you purchased? Ideally you would have let the tank run and stabilize with no livestock for a month or two.

 

[Vinman]

Remember it's only a month old. It sounds like you have a solid idea of causes for nitrate. New tanks have a lot of swings and turns at the beginning. Also check your source water. A water change is only as good as your source. Ideal would be 0 TDs.

 

[mr_noodles]

Your tank is still in the cycling process, and that's about normal. Luckily, clowns are strong (my first fish). I would do 2 sets of 20-25% water changes. I avoid anything above 30% due to such a drastic amount of change.

 

[SPR1968]

The excess food may have caused the problem, but you need to look into what methods you have in place for nitrate removal in terms of both mechanical and biological filtration. Your nitrate export needs to be either equal to or higher than import. The simple method is water changes as your doing to get them under control initially.

i assume you have protein skimmer? Look at things like Seachem Matrix/de nitrate, Nopox etc to get some ideas.

Also keep an eye on phosphate and keep it locked down very low around 0.03ppm from the start and you will avoid all sorts of issues.

I have a new system, nitrates will be strictly controlled from the very start and won’t be allowed to build up beyond around 15-20ppm from day one by various methods being brought online as and when needed