Controlling guppy fry...

Question
QUESTION: Hi, we have recently rehomed our guppies (2 males, 6 females) from a 55 gallon community tank to a (fully cycled) 30 gallon (we still need to decide on tank cleaners for this tank, but we are partial to cory cats and will probably get a few for this tank, too). I am interested in a fish or pair of fish that will help control our guppy fry population without harassing the adults. Fish with a max size of 4 inches or so would be terrific. Please let me know your thoughts.

ANSWER: Hi Tracy,

Glad to see you have more females than males! This is a recipe for success when keeping guppies, however most folks are reluctant to comply, since males are so much more colorful than the females.

There are really lots of choices, many fish will fit comfortably in a 30 gallon tank. If your water is hard, as it presumably is since your guppies are thriving (by hard I mean a pH of 7 or higher, with an alkalinity and hardness that is moderate to high on a test kit) then be sure not to include any fish that really like soft water. Blue rams, for example, are inappropriate companions because they like their water warm and soft. However certain fish which would ordinarily prefer soft water will do fine in hard water - diamond tetras, rosy barbs, and giant gouramis (I mean Colisa fasciata, NOT Osphronemus!) are fish that I have personally seen thrive in hard water as long as it is not outrageously hard. My suggestion would be for you to find a fish that you are interested in and see if it does well in your water chemistry. I have hard Florida well water (pH close to 8, off the charts alkalinity and hardness) and the only species I can't seem to get to thrive are small tetras like neons, bettas, and blue rams.

If you feel confident in your fishkeeping skills, the one standout recommendation I have for you is the neon rainbowfish, Melanotaenia praecox. Also known as the dwarf rainbowfish, it is the smallest of the garden variety rainbowfish (except for the uncommon threadfin rainbows), usually not exceeding 3 inches. They are real beauties! I believe they would compliment guppies well, and they certainly would have no problem polishing off more than a few guppy fry. The only caveat is that all rainbowfish are sensitive to nitrate. In a way they are similar to cichlids, in that they appreciate weekly water changes. If you can keep nitrates under 20 ppm, this rainbowfish is for you!

I hope that helps. Feel free to write back if you would like to know my opinion on a particular fish. It's always best to select a fish you take a shine to, research it and determine if it's a good fit for your community. I would be happy to offer my two cents.

Take care,
Nicole

P.S. As far as "tank cleaners" go, corys will eat leftover food from the bottom but will need their own foods fed to them about 5 nights a week. Shrimp pellets are a favorite, but any combination of sinking wafers or sinking pellets will do the trick. If you are looking for an algae eater, look into getting a small school of otocinclus, or the "dwarf suckermouth catfish". More here: http://www.otocinclus.com

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QUESTION: Hi Nicole - thanks for your quick and thorough response! We have done some research today and the rainbowfish seem like the perfect choice. I especially appreciate your opinion on the rams, because that was one of the fish we were considering. But now you have me thinking about adding rams to our community tank! :)

We are also in Florida but are on city water and we have moderate hardness but a pretty high ph - around 7.9. One of the reasons we moved our guppies out of the community tank is because it contains zebra danios, cory cats (they get shrimp pellets and algae wafters alternated every other day in addition to whatever makes its way to the bottom) and neon tetras who like softer, more acidic water so we have been using a combination of RO and tap water to bring down the ph and soften the water. That plus the fin nipping by the zebras made it better for the guppies to move them.

We have a bristlenose in addition to the corys in our community tank and he does a great job on the algae. We're thinking about a bristlenose plus a couple mystery snails for the guppy/rainbowfish tank. Do you have any thoughts about that?

Answer
Hi again Tracy,

You're welcome! If it's not a bother, keep on doing the RO mix, but if having to procure the RO water is keeping you from performing frequent water changes, gradually phase it out and just start using your plain tap water. (By the way, I highly recommend Prime, by Seachem, as a dechlorinator. The 50 mL bottle is a dropper bottle and makes dosing super simple - 2 drops per gallon of new water.)

I am just saying this from experience, because I remember when I used to get a 5 gallon jug of RO water from the local fish store. At the time I was doing a 50/50 mix also, but I dreaded so much having to pick up that heavy jug and put it in the truck, take it out and lug it to the fish room, etc...that I ended up skimping on water changes, doing only about 20% every two weeks. This is really not enough, even with a light bio-load. Water changes do more than just dilute nitrates, the new water adds back carbonate hardness and other trace elements which in turn makes your aquarium stable. Even if you do large, twice monthly water changes of say 50%, divide that up into weekly water changes - you'll see a difference in your fish.

If you have an RO unit right in your home, I see no problem with adding some RO water to your tank. If you intend on keeping rams,  they will certainly appreciate the softer water - unlike common community tropicals, they are often wild caught or just a few generations from wild caught. Unlike say, angelfish, many of which have been bred in Florida for ages and are accustomed to hard water, rams still seem to do much better in softer water, 78-82 F.

In fact, if you ever get any rain again (it's been a dry spell here in Central Florida...making me restless!) you may consider leaving a bucket out to collect some rainwater. I have a rain deflector - not a proper gutter - on the back of my house to deflect rain from the entryway, and whenever possible I collect some rainwater for my planted tank. This may be a cheaper alternative to RO when it is available.

Zebra danios used to drive my community tank nuts. If you care to, get some fast, schooling rasboras that stay at the top. For example, brilliant rasboras. You could also try bloodfin tetras. Putting a school (maybe 4-5) of these type of fish in your community tank might calm down the zebra danios a little. I find they get quite "bossy" if they are the sole surface dwellers, so I try to add a few others just to keep them in line. Many middle dwelling fish are annoyed by their constant hyperactivity and will end up nipping them instead!

The bristlenose would probably be fine in this tank. Since it seems like it's going to be a hard water tank, I'm not sure how you feel about adding wood, but most plecos feel most comfortable "nesting" under or around some driftwood. A small piece placed near the back or in the corner would do just fine. The snails ought to be perfectly happy in this setup - hard water is healthy for their shells. The pleco and the snails will both be very happy to have some fresh vegetables (weighed down with a rock and a rubber band, or perhaps impaled with a heavy fork...I personally use those magnetic "Chip Clips" to weigh down veggies) such as slices of zucchini, cucumber, squash, and also some spinach and romaine leaves. Other things can be offered occasionally such as shelled, cooked peas, green beans (both these veggies are easily available, unsalted, in canned form) and once in a while something sweet like honeydew melon, banana, or apple.

This web page has an extensive list of foods appropriate for fish:
http://fish.mongabay.com/food.htm

I hope that helps, enjoy!
Nicole