Here's an old post I made some time ago about cycling and this for all tanks, not just planted tanks:
The context is that someone asked about adding sugar as a carbon source to help bacteria in a new tank:
"Someone nagged me to come and say something.
I have two issues I'll address, both will be issues for some of you, but think about them and the points I make prior to responding.
I attack the idea, not the person.
In a new tank, I'm talking a new tank, did I say a new tank?
Okay, there is not much carbon, I'm not talking CO2(this is inorganic carbon, I'll refer to it as DIC), I'm talking reduced carbon(Organic carbon, the kind we eat), Fructose, glucose, carbohydrates, the types of carbon we need.
Bacteria that cleave organic N to form NH4 and by products as well as the bacteria oxidize the NH4 waste into NO2 and NO3 require not just NH4, they require a carbon source as well.
New tanks ain't got much of that.
So a little dab of sugar is not a bad idea.
It'll relieve any Organic carbon limitation that are slowing the bacterial growth rates down.
1/2 teaspoon per 50 gallons ought to do.
That being said, I am strongly and diametrically opposed to the Fishless cycling baloney. I worked in a Fish store for many years as kid.
We used the mulm from an existing tank to seed the new tank(Mulm is also a great source of reduced organic carbon, as well as loaded with tons of bacteria and fungi).
Sponge, floss, dirty gravel etc, any of that muck that is from an old tank should be added to a new tank. This adds precisely what is missing from a new tank vs an old established tanks.
There you go, immediate instant cycle.
Do not have any friends or a LFS or another tank within a few miles etc?
Buy zeolite. Only someone who had not thought things through would suggest adding NH4 to the tank.
Zeolite does not require any testing, nor any wait and after the zeolite is "spent", generally about 1 month, the tank is cycled and the media becomes colonized with bacteria, you may add activated carbon as well if you want. Unlike the FC method, you do not have to do as many water changes since the NH4 is bound and not oxidized into NO3 which needs exported via water change(more on water changes in a bit)
Zeolite is very cheap, no need to wait, no testing, no extra added labor.
A water change..........
If there was ever a single piece of advice I ever gave new folks and hobbyists, it's to do weekly water changes, good sized ones.
Especially during start up and when there are more issues.
If folks did weekly 50% water changes, they'd seldom ever have diseases or fish issues. This also applies reef tanks, but salt cost a fair amount, so there's a trade off there, smaller tanks are more likely to use that approach than a 400 gallon reef.
That held true 30 + years ago, it still does today.
If you remove the waste in the start up phase, there's no danger to begin with. The bacteria will colonize and adjust to the load over time, more water changes = less loading, thus more O2 for the fish and less NH4 over all.
More O2= faster and better NH4 conversion for what little is there by the aerobic bacteria.
Another thing about FC, the idea you add it to the tank...........
Why? Take a bucket, add the NH4 to that! Not the tank, run the filter in the bucket at high levels for 2-3 weeks, then add that cycled filter to the tank. With a bucket method, a 1 gallon bucket dumped is very easy compare that to...........
No need to coat everything in the tank with NH4 which later turns to NO3, now you have a tank full of NO3, which means what? Water change........
Which brings me right back to the beginning piece of advice: do water changes.
How many folks like to test water?
How many calibrate their test kits?
Zeolite does not require any of that if you cannot find any mulm from a tank that's established.
Why would a LFS horde their dirty mulm?
Most would be more than willing and understanding about it.
If not, you should likely shop elsewhere anyway.
Zeolite also means no waiting, you add fish, do a few water changes for the 1st 2 months, say 50% weekly and slowly add fish.
A python water changer is a much better device than any test kit.
So the smart LFS will sell them that, a tool that's useful and really saves the fish and the labor.
This hobby is successful if the new folks are successful coming into it.
If not, they quit.
Even if you assume there is something wrong based on a test kit reading, you still have to do some labor to rectify the issue if you assume there is one.
Now if you take this a step further and go into planted tanks, then we really are without any need or use for FC.
I must see about 5-10 post each month where someone added NH4 to their new planted tank and have green water algae. They overload the tank and the plants cannot take up all of and it induces various species of algae.
Plants remove the NH4 directly at lower levels and you'd be hard pressed top ever measure NH4 in a new planted tanks (or an established one).
No NO2 or NO3, no nothing. A well run non CO2 planted tanks never gets any water changes for months, sometimes years and looks a lot better than the cheesy day glow plastic plants many keep, I suggest some plastic fish to match Then you don't have to ever do any water changes or dose the fish food ever. You can sell plants, try selling old left over test kits, or bacteria or those faster growing plastic plants sometime
And the plants(well, the real ones) add O2, whereas bacteria processing NH4, use up a lot of O2 to oxidize the NH4 into NO3 which you still have to get rid and export somehow.
Happy plants = happy fish.
Water changes = good.
But the bottom line is that sugar is not a bad item to add to a brand new tank, it will speed the process up and remove the bacteria's carbon limitation.
But plants make a better solution, they add some organic carbon, they leach photosynthate(reduced Carbon) into the water column, come already pre loaded with bacteria attached to them as well as fungi etc, and they remove the NH4 directly and add O2.
Have plant eaters? Add water sprite etc to refugium or a plant filter/sump etc and add some light and you are ready to go.
If you add any or all of these: mulm, zeolite, and plants, then there's really no need for Ammonia and test kits.
Never was, but many have been hooked into the smooth talk without thinking it through to the end.
I'm not sure why really, other than bandwagon effects or maybe I'm just old school. I have the tanks, test and health to prove my results.
the idea is not bad, but the application in lieu of some very good habits that work, simpler, need to be done to some degree anyhow and make more sense seem like a much better approach.
Mulm is free, cost nothing, test kits cost $$. Zeolite is about the same as a test kit, but the zeolite will be used from then on. Test kit? Most likely not.
Good habits like water changes? That will save you for the rest of your life, test kit? Who knows, most stop using them unless there's a problem, but it is hardly preventative maintenance. The aquarist needs to do a water change anyway, so why burden them with more test kits? Think about the test, is it really something aquarist really need to do? The other thing is that these suggestions are simple and easy to understand and work more consistently. "