baby fish in a tank with large gold fish

Question
I may not be helpful at all in providing you information but i'll try my best. We have about 15 "community" fish in a very large tank. We have a three large goldfish, sucker fish, and the rest are various smaller fish. We have 3 small all black fish (don't know the name). Well we also had babies. We saw three of them (babies) yesterday. My ridiculous husband will NOT listen to me that it is no ok to just siphon water out of the tank and add water directly from the tap. This is what he did yesterday because he says that the pet shop told him they need fresh water weekly (which I don't believe). He has a pond filter in this big tank, not a regular filter. This was because when he first got them they were in a very small pond, but he refused to get a new filter, instead he bought a bigger tank. I don't think the filter is appropriate either. The water gets cloudy easily. We've only had them for a few weeks and 3 of them have died. I think the babies did already. So question one is will the bigger goldfish eat the babies of the smaller fish? And please please give me some information to give to my husband so I can save these poor fish. Thank you so much.

Answer
Hi Stacy
Sorry, but I think I'm kind of agreeing with your husband, to a point anyway lol :)  He and the pet store surprisingly(I'm not a fan of a lot of pet store's advice) are correct about doing weekly water changes.  I recommend vacumming the gravel/substrate weekly and also changing about 25% of the water weekly.  That's really the only way to keep the water quality good in a fish tank.  Plus, over time necessary minerals get depleted out of the water, and the best way to replace them is to remove the old water and add new water.  
Using tap water is also fine, with the exception if you're on city water that's dechlorinated, you must use a dechlorinator to remove chlorine or chloramines that the water companies add to disinfect the water.  If it's well water, usually there's no need to use a dechlorinator unless you have heavy metals in the water.  

As for the babies, yes the goldfish as well as the other fish may eat them.  If they're small enough to fit in a fish's mouth, they will be eaten-unless the babies/fry are good at hiding.  They also can be sucked up into the filter intake tube.  You can buy a small breeder's net, Walmart has them also for about 3 or 4 dollars.  It's a mesh net that hooks onto the side of the tank, and you put the fry/babies in there till they're big enough for the regular tank.

As for the filter, it's probably ok to use, especially if it came from a small pond.  Most filters do 3 things, biological, chemical, and mechanical filtration.  The biological is surface like bacteria bio balls or even the filter pad, beneficial bacteria grows on those and converts ammonia and nitrites into somewhat non toxic nitrates.  Chemical filtration would be if there's any carbon used in the filter-this isn't always necessary to use.  And mechanical filtration-which for the most part is what all filters do, you put the filter pad or filter floss in the filter to collect the larger solid particles that flow into the intake tube.  So, at the very least I'm sure your filter is providing mechanical filtration, and most likely to some degree biological filtration, so it's probably ok.  

Now, you mention the water gets cloudy, what color cloudy?  If it's white/grey color that's most likely a bacterial bloom, meaning there may be ammonia present in the tank.  If it's a green color, that's free floating algae, and the filtration actually may not be enough for the larger tank.  Or, another possibility, the tank may be overstocked-which is very easy to do with goldfish.  Not sure how large your tank is, but with 3 goldfish, you should have a minimum of 45-50 gallon tank.  Factor in the other fish, and I would say you should have a minimum of 55 gallons, and without knowing what the other fish are, how large the goldies and the sucker fish are, that still may not be enough really.

So, the question is, what type of filter is on there-brand name and model number if you know it, because I can try to look it up to see if it's good for that tank size?

How large is the tank?

How long has the tank been set up?

And, do you know what the ammonia, nitrite, and nitrate readings are?

Christy