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Cycling questions

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We just upgraded our tank. The first tank unfortunately cycled itself so I have no experience with 'assisting' cycling. I was so frustrated and worried about the old tank because something in there was making them sick, that I just wanted to start again and not risk transferring any drama to the new tank. I threw out the media which was old and awful looking anyway, and now we have to start again.

I fully understand the cycle and the cycling process I'm just not sure of the best way to approach it for this tank.

We just built a pond filter and the combined water volume of the tank and filter is at minimum 700L. I have 3 fish, the largest is about 11cm sl. That's about 233L per fish.

It seems like it would take a really long time to get the ammonia concentration up in that volume of water? I'm assuming that means that the tank would take a lot longer to even start cycling. This normally wouldn't bother me as long as the fish were happy, but we're going away in 6 weeks.

We've worked out a plan for a contunous water change, so if we begin a fish-in cycle, is the large water volume and continuous water change enough to keep ammonia etc down to suitable levels while we're away? I realise it'll probably slow the cycling process but that part is more about keeping the fish happy while we're gone. As long as the fish aren't in danger I'd prefer to do this.

I guess I'm asking whether the water volume and constant water change is enough to keep everyone happy despite not having a fully functioning cycle? We'll also have plants in the tank, although not a lot of them as we're doing a test run to determine which plants aren't considered lunch before we plant the whole tank. The pond filter will also have plants on top to help with nitrates.

Would it be better to do a fishless cycle and try to get it done more quickly?

Any other ideas?

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We often, incorrectly,  refer to a tank as cycled or not cycled.  In fact, we should specify that a tank with stable ammonia/nitrite readings of zero  has completed cycling for that fish population. It has grown the largest population of nitifiers that can survive on the amount of ammonia produced by the fish.  Many of those nitrifiers exist in an inactive state in which they carry out just enough metabolic activity to stay alive, but can neither grow in size nor reproduce until they get fed.  Centuries before water testing or the invention of the misleading term "cycling", people knew that if you set up a new pond and immediately added a full load of fish, the fish would get  sick and often die.  So they learned to start out the pond with very few fish (adding additional fish very slowly) or very small fish.  To this day, the overwhelming of pond keepers use this procedure for cycling new ponds.  


I call this procedure "cycling by severe understocking" and consider it the fastest, easiest, and safest way to cycle a tank/pond.  To explain the fastest part, excess ammonia and nitrite both inhibit nitrification.  "Excess" means more ammonia/nitrite than the nitrifiers can use.  How do you know you have excess?  You get non-zero readings of ammonia/nitrite.  This means you have more ammonia/nitrite in the tank than the existing population can "eat".  Nitrification rates slow as the concentration of ammonia and nitrite in the water increase, a process known as substrate inhibition.   "Substrate" in this case means the substance you start with in a biochemical reaction -- ammonia and nitrite.  While as little as 1 ppm ammonia can measurably slow the rate of nitrification, it won't make much difference in how long it takes to cycle the tank.  


I recommend the following.


Set up the tank, water change system, and filter.  Put in all of the plants (in pots for easy removal of the ones you don't want) which will certainly have some nitrifiers on them to seed the tank.  Add one fish.  Test the water for ammonia and nitrite every two days.  After a week of zero ammonia/nitrite, add the second fish.  Again test every two days.  If ammonia/nitrite stay at zero for the full week, add the third fish.   Continue testing a couple of times a week for a month, and then relax.  For your water change routine and fish load, the tank has cycled.


What I have experienced myself or read in other people's posts here indicates fishless cycling takes at least twice as long as properly-conducted fish-in cycling.  I think this happens because of the excess ammonia typically used in fishless cycling.  I have been trying to collect  information from people doing a fishless cycle keeping ammonia and nitrite below 1 ppm to see if this speeds the process. 

Edited by shakaho

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That's a fantastic explaination Sharon, thank you. I had read about avoiding 'excess' ammonia/nitrite because of the inhibition but assumed it was referring to having levels above the amount that's aimed for during controlled cylcing. Your explaination makes perfect sense as always.

When we get back we'll be looking for more fish, I can only quarantine so many at a time so I'd planned to add them to the tank in small quantities anyway but I'll follow your plan then too.

I can't tell you how much I appreciate your help. You've spent so much time answering my millions of questions over the last few months and I'm sure it looked like nothing was happening at my end, but it is. It's just slow. My bf jokingly rolls his eyes every time I say 'Sharon says....' :)

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