The Silent Cycle. Sort of.

My plans are coming together and it is time to put some fish in the 120. I will start with some Gambusia, or mosquito fish, which were collected locally and live in a large tub on my deck, eating mosquito larvae. This has definitely made a dent in the mosquitoes we encounter outside.

I put 7 full-bodied females in the tank, and the next day I took the gunky Filstar XP3 off the goldfish tank at work, which is a 45 gallon and houses 5 fan-tailed goldfish about the size of walnuts or ping-pong balls. I figured the filter, which has not been cleaned in a while, would have more than adequate biobugs for the Gambusia. I brought it home and removed one of the clean XP3's off the 120, swapping it out for the dirty one from work. I then put the clean one on the 45 at work for the goldfish.

Typically in a well established tank you can literally replace the filter completely with a brand new one without showing signs of a cycle. I would not do this on a tank that was set up less than 6 months ago, though, because it is easy to cause a mini cycle by this type of disruption. I have even created a mini-cycle by being too aggressive cleaning substrate in a tank that was younger than 6 months. The 45-gal at work has been set up and stable for a year.

Cut to 12 hours later and I tested the water. I typically don't do this when I seed on a massive scale like this (using the whole filter off of an established tank with a heavier bioload than the new tank), but I was having a discussion about silent cycles and seeding new tanks on the CVAS forum, so I wanted to document how a silent cycle might progress. To my surprise, I found 0.25 ppm NH3, or ammonia. There was zero NO2, or nitrite, and 5 ppm NO3. The fish appeared perfectly normal and happy, and the water was crystal clear.

12 more hours pass and I'm getting the same readings. I started to wonder about my so-called "silent" cycle, and was surprised that I was seeing the ammonia, though a low reading. I don't like seeing ammonia at all, since any exposure at all can be permanently damaging to the gills of a fish (Reference Here). I decided to take action, though I could have waited another day, perhaps. I think this kind of thing is typical, but since when I do my usual seeding procedure I never test the water and everything works out peachy. I go by the appearance and behavior of the fish, and have never had a problem to date, so it never occurred to me to test the water right after the new tank is seeded.

Anyway, I took some gunky filter sponges off my snail tank filter (AC30) and squeezed that goop into the 120, which clouded everything up, of course, but, lo and behold, 12 hours later I was showing zero ammonia, zero nitrite and 5 ppm nitrate. The cycle is done!

However, this is not the time to stock willy nilly. Patience is required, especially at this delicate point. The tank is very vulnerable to a mini cycle now and I must be careful not to disturb the decor, substrate or filters for several weeks, at least - the longer you wait the better. I will add stock, though, since I'm not going to keep the Gambusia in this tank - they're needed back outside. Our warm weather can linger well into October so mosquitoes will be with us for a while to come. I'll be replacing the Gambusia with the Denison's Barbs soon, since the ones I'm looking at are about the same size as the Gambusia, and will have almost identical bioload.

After they're settled in for a couple of weeks I'll add a few angels, but I might add about 6 angels at once and add more seed material at that time for insurance. These angels are still small, about quarter to half-dollar size in the body, but when it comes to cichlids they can be territorial, so adding one, then another, then another later on might be a bad idea - the newcomers will almost certainly be bullied by the ones already there that have set up a territory.

Since I have so many established tanks up and running right now it won't be hard to get more seed material when I add the angels. MTS is paying off!