Worried about danio behaviour in two-month-old tank

[mikeu]

Hi,

I'm new to this forum, having just signed up to ask this question! We had a small tank for awhile when I was a kid, but the past two months have been my first real experience with trying to maintain an aquarium.

I have a male leopard danio who has started to appear quite lethargic over the past couple of days, and I'm starting to get worried. I can't see anything visibly wrong with him, although he does look very slim, but he hasn't really been eating (that I've seen). He tends to just hang out in a corner of the tank near the top, either swimming in place or in slow circles. He seems to be able to swim fine when he chooses to, that just isn't very often. There's no visible damage to his body or fins. I've seen him approach food, even stick his mouth to it, but as I said I haven't seem him actually eat in a few days.

My tank is 21 gallons and has been set up since the beginning of March with live plants. Mid-March I added the first fish, a pair of leopard danios. At the beginning of April I added a swordtail and a rainbow shark, as well as three assassin snails because a pest snail population had started. About 10 days ago I added a dwarf bristlenose pleco who unfortunately only survived for three days. I think the tank may have been too hot for him. The rainbow shark is the only one who appears to have already grown -- he and the swordtail are both about 2-2.5" and the danios are more like 1", although the female is quite a lot fatter.

I've got a lot of green algae right now, it's been growing steadily for about two weeks. I've removed some stringy stuff from the water by hand, and scraped some off of the glass, but probably need to do a more thorough removal soon. I had hoped that by adding the pleco, and then later some more fish, the plants and fish might reach an equilibrium that didn't allow the algae, but especially after the pleco died I haven't continued down that path yet... I'm also not sure how healthy the plants are, since some of the bushy ones (cabomba, I think) are turning a reddish brown at their tips. The leafy ones appear to be healthy though, as far as I can tell.

My ammonia and nitrite levels are both zero. The pH is quite high, right at the top end of my API test card's scale at 7.6, but has been steady since the first fish were introduced. The temperature varies between 26 and 29 C most days (~78-84 F). Occasionally it goes above 30 C (86 F). When it was first set up it rarely went below 28 C (82 F), and I have been working hard to bring the temperature down but haven't found a good solution. Until the pleco, none of the fish seemed to have any problems with the environment. The tank is in a bright room, but receives no direct sunlight. I have the fluorescent lights on for 12 hours a day for the plants, and it is on a timer.

I have an AquaClear30 fliter that is capable of between 50 and 150 gph flow rates. I have been keeping it at its max flow rate, and haven't changed any of the filter media yet.

I have been removing 2 gallons and adding 3-4 (with tap-water conditioner) every one to two weeks. The last one was 10 days ago. I do my best to vacuum the gravel during changes, though it's hard to get the vacuum under the plants so I'm mostly able to do it well at the front of the tank.

I've been feeding the fish Nutrafin Max flakes that came with the tank.

Hopefully that's enough detail, but please let me know if there's anything else I should add! At this point I'm primarily interested in the male danio's health, but would also appreciate any comments or advice on the algae, temperature, plants, or anything else that you more experienced aquarists may have to say about my setup.

Thanks!

Mike

 

[librarygirl]

Hi! I'm still pretty new to all this so I probably can't diagnose your issue but I have some starting questions:

You mentioned no nitrites or ammonia, what about nitrAtes? If you set up your tank and added fish 3 weeks later, your tank probably isn't cycled? If it isn't cycled and you're only doing water changes once a week, that could be big problem #1. (If you're not cycled, or not sure, you might want to give this a read)

Also that seems like a lot of temperature fluctuations to me. Do you have an adjustable heater in the tank? Do you match temp when you do water changes?

That's all I can come up with. I'm sure someone more experienced will come along soon to help.

 

[alLexX]

i see 2 things wrong,first,the rainbow shark needs a 55 gallon tank at the minimum,and the danios are schooling fish,so get at least 4 more.

 

[mikeu]

Thanks for the replies.

I don't have a nitrate test kit; I suppose I'd better get one. The reason I started with only two danios in a 21 gallon tank was that I was cycling it with them. The filter ran for a week before they were introduced, with just the live plants in the tank, and then I started to slowly add fish a couple of weeks later. I do plan to increase the number of danios over time.

The temperature fluctuations seem large to me too, but I'm finding it hard to manage them because we are in a top-floor apartment and room temperature is often dependent on what those below us do with their heating. I've got an adjustable heater in the tank, but it's set to around 24-25 C so basically never engages. I only try to temperature match during water changes if the tank temperature is closer to 26 C; when it's up around 28 I take the opportunity to cool it a little bit with the replacement water.

That's really good to know about the rainbow shark, too. Given that I'm not going to be upgrading to a 55 gallon tank anytime soon, what do you recommend as the best course of action? Try returning him to the aquarium store? How long is it likely to be before the smaller tank becomes an issue for him (and/or the rest of the fish)?

If nothing else, I'll start doing water changes more frequently and get the nitrate test... Thanks again!

 

[alLexX]

Thanks for the replies.

I don't have a nitrate test kit; I suppose I'd better get one. The reason I started with only two danios in a 21 gallon tank was that I was cycling it with them. The filter ran for a week before they were introduced, with just the live plants in the tank, and then I started to slowly add fish a couple of weeks later. I do plan to increase the number of danios over time.

The temperature fluctuations seem large to me too, but I'm finding it hard to manage them because we are in a top-floor apartment and room temperature is often dependent on what those below us do with their heating. I've got an adjustable heater in the tank, but it's set to around 24-25 C so basically never engages. I only try to temperature match during water changes if the tank temperature is closer to 26 C; when it's up around 28 I take the opportunity to cool it a little bit with the replacement water.

That's really good to know about the rainbow shark, too. Given that I'm not going to be upgrading to a 55 gallon tank anytime soon, what do you recommend as the best course of action? Try returning him to the aquarium store? How long is it likely to be before the smaller tank becomes an issue for him (and/or the rest of the fish)?

If nothing else, I'll start doing water changes more frequently and get the nitrate test... Thanks again!

im not sure when the tank will become an issue,but i suggest rehoming it,either to a friend or a good petstore.if you can,a friend with a big enough tank would be better,that way the store cant sell the shark to someone with a smaller tank.also,its not so much a matter of bioload,but the temperament of the fish.they claim a large territory,but in a 20 it cant claim one as big,which can stress it out.