Stocking and nitrates

[Sinbad633]

Hello,

I've two questions concerning stocking and about nitrate levels:


In the tank so far, which is 125L, 80cm long:


8 Cardinal Tetra

4 Honey Gourami

1 German Blue Ram


The tank has 0 ammonia, 0 nitrite and 3ppm nitrate. The nitrates don't really seem to rise. The tank has been stocked to this level for four days now and I've been testing everyday. I am surprised the nitrates aren't really rising, there are quite a few plants in there. Are they using them? The tank was cycled fishless beforehand, the ammonia and nitrite have not budged off zero so things are happening. Should I expect the plants to remove most of the nitrates at this stocking level?


I would like to add a few more fish in the fullness of time. I was considering another GBR, but a friend of mine found his first one would die from stress after adding a second. Perhaps from territorial disputes.


I would like to add 6-8 black phantom tetraonce the present incumbents have settled and I'm sure I'm not going to get a mini cycle. I'll give it a month or so to be sure. I haven't found anything suggesting these maybe incompatible but I'm always open to greater knowledge.


Would anyone have any suggestions for any other species that would work? I'd like to keep the tank under stocked by a small amount overall.


Many thanks.

 

[Byron]

On the nitrates. With live plants, nitrates should be low, and many find them at zero. My tanks are well stocked with fish, but nitrates remain in the 0 to 5 ppm range using the API liquid test, and this has been the case for many years.

The reason is largely because aquatic plants prefer ammonia/ammonium as their form of nitrogen. Fast growing plants, particularly floating plants which are about the fastest growers in an aquarium, can literally be called "ammonia sinks," because of the amount of ammonia/ammonium they can take up. This is why many of us do what is termed a "silent cycle" in new tanks, allowing the plants to use the ammonia rather than going through an artificial cycling. Plants taking up ammonia does not produce nitrite, so the Nitrospira bacteria are fewer, and that means they are not producing nitrate. This is why you see low or no nitrate. The nitrifying bacteria will still establish, you just won't see it with tests.

Plants will also use nitrate, and it seems nitrite too. Some plants do actively take up nitrate, but most prefer ammonia/ammonium. These will only turn to nitrate (or nitrite) if ammonia/ammonium is deficient. The reason is that they must change the nitrate back into ammonium in order to use it as nitrogen, and this takes more energy from the plant so it is sort of a "last resort."

So, nitrates should (and hopefully will) remain low. Nitrate is toxic to fish, just as ammonia and nitrite, but less immediate. Nitrate levels in the habitat waters are rarely if ever much above zero, and the physiology of fish function best in such conditions. Unless you have nitrate in the source water, keeping it very low in an aquarium is not difficult; the fish stocking/feeding is the source so not overstocking or overfeeding along with plants should keep nitrate very low.

Now to the fish. Adding more fish should not cause any form of mini-cycle, because of the plants ability to take up so much ammonia/ammonium. BTW, ammonia changes into the harmless ammonium in acidic water; plants and bacteria take up which ever is present. [Plants convert ammonia to ammonium just as they do nitrate, but we needn't get into that.]

You have space for more fish, if you select them carefully. Keep in mind that you have warm water species...rams need 80F minimum; the cardinals can manage with this easily. The Honey Gourami are at the top end of their range which is pushing things for them. The other issue is activity level. These fish are all sedate, not active swimmers, so tankmates must be the same. Active fish in a tank with sedate fish unnerves the sedate fish, causing stress which means weakened fish.

Black Phantoms are sedate fish, remaining in the lower half/third...which is where your cardinals and ram will live. They too would be at the upper end of their temperature range. But you might want to consider upper level fish to balance things more. Hatchetfish and pencilfish immediately come to mind as sedate, peaceful upper level species.

The hatchetfish species in the genus Carnegiella [Black-wing, pygmy and marble] are the smallest, and remain right at the surface almost exclusively. They would be at the upper end of their temperature range, but should manage (being at the surface does help in this a bit). The larger Platinum Hatchetfish, Thoracocharax stellatus, loves warmth, 80F is mid-range for this beauty. It tends to remain just below the surface by a few inches, except to feed. It is more interactive than the other species (I have or have had all of them) but not such as to be disruptive; I have never observed interactions among a species of hatchet like this one, it is indeed a truly lovely hatchetfish; a group of 8-9 would be fine. Some floating plants are necessary, but floating plants should be part of any tank with forest fish. Cardinals will always be more settled and colourful with plants over them.

Among the pencilfish, Nannostomus eques remains near the surface among floating plants, is very peaceful, and swims at an oblique angle for interest. The temperature is its upper limit. Another pencil, N. beckfordi, is also upper level, but I do not recommend it here. This is a very feisty species, and territorial; nipping other fish that approach the surface is common.

Last, on the second ram. Not a good idea. In huge spacious tanks (more than 4 feet) you could probably get away with it. Male rams are obviously territorial, so space is needed. But another thing is that male/female must select each other and bond. If not, they may get along, sort of, or they may not, but at some point one of them will have had enough and kill the other. If you select a pair from the tank of fish, and can see that they seem to have accepted each other, you should bee OK; but otherwise, stay with the single ram.

Hope this helps.

Byron.

 

[Sinbad633]

Many thanks for your long and considered post. Much appreciated and has given me plenty to think about.