Calculating the amount of fish to add after my fishless cycling is done

I have about 1200 gals of water in 2 fish tanks I am mid way in fishless cycling— asking how many fish to add to the tank to start off I have read all kinds of ratios but not idea of the difference in how much NH3 I have added to start to how many fish that is to start------ guess it is better to start small and grow add 25 fish at a time as the system grows ? JD

You usually want to add between 25 - 40% of your total fish load in the first addition for a new system. Then at the rest once the system has had 2 - 3 weeks to finish cycling.

Additionally, constant water quality monitoring after adding fish into the system will be key to ensuring that your water quality (Ammonia, Nitrite, Nitrate) are all within acceptable levels for the species of fish you are planning to raise.

Specifically Ammonia (un-ionized) and Nitrite are extremely toxic to fish and therefore if these levels exceed tolerable concentrations for the species of fish you will want to do a 25% water exchange each day until the levels stabilize a bit.

Jdusci I have been doing a fishless cycling start up and am ready to add the fish— please, I do understand the toxicity… and the whole point is to add fish in increments so as not to blow up the system with too many fish at once… my concern is my local source has fish in 2 sizes can I add Nile Tilapia and 60-90 days later add a different size --concerned that the new fish may be smaller…

@jamesgang Great, can never be too careful with monitoring WQ, especially when adding new fish!
In terms of the two different sizes, I think your thought process of getting the smaller size initially and then growing them out and then adding the larger fish at a later date is correct. I would just monitor the first batch of fish closely and once they are a similar size as the larger fish offered locally then go ahead and add in the second batch. You can always take a population sample to get a rough average weight/size of the fish to be a bit more precise. However, always use good handling techniques when touching/weighing fish to avoid any potential disease issues.
All the best,
Josh Dusci

JD wouldn’t even think of handling tilapia with gloves!! getting that slime off of bare hands is just nutty hard— makes them a real project to filet too!