Kill the hydra or leave it alone? - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 3 Old 01-31-2010, 03:04 PM Thread Starter
Kill the hydra or leave it alone?

I have hydra in my tank, as I posted in a recent thread, and I have been doing lots of research to see what the causes and problems could be. Well, here are some bits and pieces of info that I came up with:

1. I can kill them off with a very low dosage of fenbenzadole (a dog de-wormer) with no side effects to the tank

2. they feed off copepods so they often have a population outburst after a copepod outburst (don't know if I have those in my tank or not!)

3. they like live foods, like fry, and kill them by stinging with their tenacles

4. they are harmless for most fish (esp. gourami who like to eat them) but are unsightly

5. my over-feeding habits probably contributed to the hydra population growth (it's in both of my tanks and i just introduced brine shrimp so i'm guessing they are eating leftovers?) One other correlation of when the hydra appeared is that I started doing larger and less frequent water changes.

If I kill them with fenbenzadole, am I masking a larger problem with my tank? Should I leave them alone and let nature take care of them? Or are they actually correcting a problem with my tank that, without the hydra to keep it in check, will get out of control.

Stephanie's updated tank profiles:
29 gallon 10 gallon
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post #2 of 3 Old 02-01-2010, 02:07 AM
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If I kill them with fenbenzadole, am I masking a larger problem with my tank?
Yes. While that product may not harm the tank or the biological system inside of it, it may indeed be lethal for your fish, and for sure would kill any inverts in the tank. I am not sure if that is one of them, but many of those types of medications leave residue in the tank after treatment, which means long term low/tiny amounts leeching back into the water column for a long period of time, and it also means that tank would always be unsafe for any type of invert, such as shrimp. Those types of medications will also kill snails. I would definitely not use that product/medication in your tank.

Should I leave them alone and let nature take care of them?
Yes and no. Yes, let nature take care of them, but help it along in other ways... such as finding the cause of their population explosion and fixing the cause of the actual problem. The appearance of them is a symptom of a larger problem. If you resolve the original problem they will go away naturally. Getting on a good maintenance routine is a good start. 30% water change once/wk is a good schedule for most tanks, provided they are not overstocked with fish or overfed. In a situation where water quality may be in quite bad status (if you post test results for ammonia, nitrite, nitrate, pH then we can help sort that out) or where the water chemistry in the tank differs greatly from the source water being used for water changes, then 10% every day for a few weeks is a better schedule until all is in good standing. Be sure to gravel vac once/month, and the first one should be done with the next water change. If there is an extreme amount of food/organic waste in the tank, gravel vac can be done with each 10% change daily until the entire substrate has been covered.

Or are they actually correcting a problem with my tank that, without the hydra to keep it in check, will get out of control."
I would not say they are correcting a problem, simply reacting or thriving in their proper conditions. What is proper for them is not usually proper for the fish, so there is the indication of the actual problem. As I explained above, if the original problem goes away, they go with it. When feeding the fish they should be able to completely consume the amount of food you offer within 1 - 2 minutes (if you have bottom feeders I would give it 2 minutes). If there is excess food in the tank beyond this time it should be removed. This can be done with a siphon hose, airline tubing, or a turkey baster. Also remember to change any carbon in the filter every 30 days.

Proper maintenance and feeding practices should resolve this problem for you. Unless you have fry in the tank, be patient but diligent. Your fish are going to thank you!
I hope this helps.

Dawn Moneyhan
Aquatics Specialist/Nutritionist
Juneau, WI
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post #3 of 3 Old 02-01-2010, 11:17 AM Thread Starter
Dawn, thanks so much for the reply, and I always appreciate your consistent thoroughness.

I've read several claims online whereby people use small amounts of the med (.1 grams for several sized tanks) and it kills off the hydra with no negative consequences to the inverts in the tank (many varieties of shrimp)...I'd actually have to double check on the snails, though. This is one of those meds that vets will prescribe to dogs "just in case" because it doesn't hurt anything, really. But if it kills hydra, why wouldn't it kill the snails, right?

I would, of course, rather treat the problem at its root, which I believe to be at least in part due to overfeeding. I can correct this problem in my community tank fairly easily, but my dwarf puffer tank is the problem. I have a ten gallon with three DP and a few shrimp (that were raised in the same tank as the DP which is why I think they are still alive). Well, I feel like I have to feed them plenty of brine shrimp or blood worms (which is what I normally rotate for their feedings) and if I don't put an abundance in the tank then they won't find it. But it's hard to get out all of the leftover. Can you recommend another feeding strategy?

My water params have been really good in both tanks...ammonia and nitrite of course always at zero and my nitrates always under 5 ie. barely traceable (probably because they are planted tanks). pH is around 7.4 in the DP tank and 7.8 in the other (the variation being large pieces of DW in the DP tank, I don't alter the pH on purpose).

There are a few factors that have changed over the last couple of weeks that may have affected the tanks: 1. feeding brine shrimp (both tanks) has been a new thing since I got the DP's a couple of weeks ago 2. I switched from two pwc per week with thorough gravel vac to one pwc per week without as thorough gravel vac 3. introduced several new plants from an online store (this may have introduced it but has nothing to do with perpetuating the problem)

Also you mentioned changing the carbon I actually don't use carbon in my filter as I've read that it is unnecessary and may remove things that are critical for plant health. If I treated the tank with meds I would use carbon to remove them and then again remove the carbon. Any thoughts on that?

I have thought that perhaps frequent pwc until the problem resolves would be a good approach (but my water params are similar to the source, all same pH except my tap has ammonia). This would mainly be so I could gravel vac and remove potential food sources for the hydra.

Stephanie's updated tank profiles:
29 gallon 10 gallon
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