This guy and his girlfriend I know started a small community tank about a month ago. I explained about cycling the tank and he borrowed some books from me. He read the books and researched on the internet. I offered to run a small filter on my tank for them but they never bothered

So they go out and buy some danios and some barbs(not sure which sort) and some neons. Unsurprisingly the neons died. Two weeks ago I put a small internal filter on one of my tanks for him. Their tank still isnt cycled but the danios and the barbs are still alive. He tells me his test results are not good. When would be the best time to take the internal filter that is running on my tank and put in on theirs?

Difficult to say exactly when you would have a really good bacteria colony. However, I would reckon that running a filter on your tank for three weeks would certainly start a colony off. Could be earlier than that, but I would leave it for three weeks. I wouldn't like to bet that it would be fully cycled though.

If he hadnt set up the tank I would of suggested a month but given that it is set up and he is getting high test results I thought earlier would be better with a partial colony to try to save the fish he has. Just wasnt sure how early. I will leave it another week then.


As usual OFL you are a great source of information!!!!!

When I said three weeks, that is just the rough guess. I'm just going by how long it takes to cycle a tank from fresh. If it takes six weeks to cycle a tank, I would expect you to have a colony within three weeks if you are doing it on a cycled tank. I'm sure other people will pipe up if need be.

What kind of filter or is it, is it the underwater filter like a small fluvel?

Its an old rena internal filter with just a sponge in it. No other media


I thought that if a tank is set up and cycled then if you put another filter running on it the added filter would quickly pick up a colony of bacteria from the tank.

I've tried exactly what you're doing delboybully and it didn't work so well. The reason I figured was that the fully cycled aquarium already has a good balance of bacteria in the system and there just wasn't any need for the bacteria to multiply and colonize the new suface area in the new filter. I just ended up jumpstarting the aquarium the old fashioned way. That is, by taking a piece of another bacteria colony and bringing it to the new aquarium. Nowadays I do that by swapping biowheels. Back in the day, I'd gently remove some of the gravel from an established aquarium, clean it off in a bucket full of the new aquariums water, and them dump all of that (water and gravel) back into the new aquarium. In this way you know for sure that you are introducing bacteria and spreading it over the maximum amount of surface area. I'm not sure whether or not this actually helps the cycle. I'm convinced that each cycle just has to happen on its own. But this certainly couldn't hurt to try.

Mneilssen, I agree with you that the best way to go is to use some media from my filters. However the problem is he only has a sponge filter and its an odd design. It sits in the top of the tank and a pump pumps water up which then drops through the sponge(some cheap chinese design). This make is incompatible with my fluvals

The next best thing I thought was to run this old filter on mine for a while and then place it in his tank. It cant do any harm I suppose

As for using some gravel and tank water from mine, I thought this was a waste of time as there isnt much bacteria in the gravel and water as most of them live in the filter

delboybully wrote:


This could be the case. Especially if your tank is lightly stocked. It's not like the bacteria seek out your filter to live in though. The bacteria in the filter simply have a better O2 supply and are able to outcompete other bacteria for food. This makes them the most important bacteria pound for pound in the aquarium. The nitrifying bacteria that you want in the aquarium are the type that cling to surfaces. To some degree, they are on every surface in the aquarium. They just function better where there is more O2 to utilize. Generally, that's going to be where there is water flowing quicker. I've got a feeling that these areas also take the longest to colonize.

I guess there would be one way of knowing how much bacteria you've got in your gravel. Ask yourself this question. Have I every had a small spike in ammonia after getting a little too carried away when I cleaned the gravel? If the answer is yes, then you've got a thriving gravel colony.

I've always looked for ways to jumpstart a cycle. The only way that ever really worked was taking an old filter and using it on a new tank. That is, I took it directly off of the aquarium it was running on and put it on the new one. The newer aquarium never did have an ammonia spike. However, the old one's levels did go through sort of a one week mini cycle having replaced one of it's old filters with a new one.

I've used tank gravel transfers to smooth out especially rough cycles before. It may have helped keep the ammonia from getting too high. In this case the ammonia was 6ppm when I used the gravel, but who's to say that it wasn't about to drop anyway? I've seen ammonia at or above 8ppm in new tanks before. I'm just convinced that every cycle is going to be its own little beast.

Good point, I never thought of it like that. If some bacteria are living in the gravel then by moving some gravel to a new tank you will introduce that bacteria to the new tank which can only help the new tank cycle


I only test for ammonia about once a month as it is always 0. Gonna do a test after the next gravel clean to see if I get a spike

You shouldn't get any kind of ammonia spike if you keep your gravel clean. Remember that normally ammonia will be only present in a cycled aquarium if you are overfeeding, left food in the tank, not noticed a dead fish, got too many fish. Keep your gravel clean, and you shouldn't have any problems with ammonia

OFL thats what I thought, however

MNeilssen wrote:



So does this mean that there isnt much bacteria in the gravel and if so then is it really worth adding it to a new tank to help with the cycling process?

OFL - This is where you and I are always going to disagree. You are going to stick with very conservative stocking levels. I'm always looking for a way to maximize biological filtration. You may have a point with cleaning the substrate, if the substratum is sand. The majority of sands surface area is in contact with other sand. Bigger pieces of gravel have more water between them. That's valuable real estate when you're stocking heavy. I'm talking about this the wrong way though. Let's look at it this way... If you were to clean your entire aquarium in one day (that is; substrate, glass and filter) you would be adversely affecting your biological filter. If for some reason you were able to do all of this without ever noticing the nitrogen levels fluctuating, (through testing! not cloudy water or sick fish) then you've either done a poor job cleaning or you've got more aquarium than you need. There's nothing wrong with having more aquarium that you need. So long as you can afford it.

I'll add this too. If the fish keeper doesn't have the time or the motivation to keep up with the water, then having the most amount of aquarium and the smallest amount of fish is ideal. The more water you've got, the more time you have to make changes when things go wrong. If you've got the time and the diligence, anything is possible. After all, we're really first and foremost keepers of water. The life within is simply the payoff. Nano reef systems are a stunning example of this philosophy.

delboybully - the nitrifying bacteria exist, in some degree, on EVERY surface in the aquarium. The onyl way you are going to know if this is worth it or not is to give it a shot.