Hello all,
I am currently cycling my system in preparation for one O. bimaculoides. The tank contains 10lbs of live aragonite sand (which has been in the tank for 4 weeks), and three damsels (present for two weeks). I have been testing the water daily using API pharmaceuticals saltwater master test kit, but have not yet seen any increase in nitrite, nitrate or ammonia levels. Admittedly I have only been testing for the last week, but surely I won’t have missed the cycle? The water quality has been consistently as follows over the last week:

Nitrate <5.0mg/L
Nitrite <0.25mg/L
Ammonia <0.25mg/L
(These three measurements are calorimetric. All three are very close in colour to the “0” level on the colour chart, but I do not have precise values).

pH 7.97 – 8.08
Salinity 1.026 spec gravity (36 ppt)

The system is 80 gallons total (one 40G tank for the animals, connected to a 40G tank for water conditioning) and I have two 4-stage reaction canister filters and an under-gravel filter (with 50lbs of crushed oyster shell), through which the entire 80 gallons passes every hour, at least.

I would be very grateful if someone could give me an idea of when I might expect to see the nitrate, nitrite and ammonia levels rising, and to what level they might be expected to rise,.
Thanks!
Lene.

There's no way to tell how high the levels will go. As long as there is ammonia present the cycle will continue until you have a stable colony of bacteria.

You'll need to remove those damsels before you get your octopus if they are in the display tank. By then they will have established their territories and they don't care how big or bad any trespasser is, they will attack it and they can do some serious damage. I assume the under-gravel filter is in the filtration part of your system. If it's in the display your octo will dig it up. Otherwise you sound pretty good to go. Just be aware that you'll need to maintenance the canister filters and vacuum the crushed coral regularly as they can harbor detritus and if they're not taken care of can become nitrate factories.

Please don't use live fish to cycle a tank, it is cruel and unnecessary. You can create an ammonia spike with grocery store shrimp or old fish food.

As for how long it takes, that depends on whether or not you inoculated the tank with bacteria. You can do this by adding substrate, filter media or water from an established tank. As for how long, its going to take as long as it takes. For reference I just cycled a small tank using water and sponges from another tank of mine and a big handful of pellet food and it took a full month. If you didn't add bacteria culture then it may take longer.

The numbers you are looking for aren't specific numbers so much as a big rise in ammonia then a drop to zero. The a big rise in nitrite, as in whole numbers not decimals, and then a drop to zero. If you are getting a reading above zero for either ammonia or nitrite then you tank is not yet cycled. If you want to see this in graph for search "tank cycle" or "nitrogen cycle".

erin

It is likely that running your filteration during your attempts to build ammonia is keeping the tank from coming through a solid cycle. You might add a frozen shrimp and turn off your filters. You will still want water flow so if your filters are integrated into the water exchange, remove the filtration material. If you try to add fish at this stage, thinking you have cycled the tank, you will likely experience what is known as new tank syndrome. If my assumptions are correct, you currently have a minimum amount of bacteria and your filters are handling the existing bioload but this will fail when you try to introduce additional creatures.

You might add a frozen shrimp and turn off your filters.

Thanks so much for the advice. I will remove the damsels, add some frozen shrimp and turn of the filters right away (and then try and be patient!).
Cheers,
Lene.

Thanks so much for the advice. I will remove the damsels, add some frozen shrimp and turn of the filters right away (and then try and be patient!).
Cheers,
Lene.

The expression, "nothing good happens quickly in a marine tank" is a motto you need to repeat when you get over anxious.