How many is too many?

[pugsandseals]

We have a 180 litre tank which was started up in January. We have hard water so started with 2 zebra snails & 3 Assasin snails, then added some guppies (2 male, 4 female) & platys. All doing really well now, but the guppies are breading like rabbits! We have at least 15 babies at various stages upto 2 months old.
My question is, how many are too many? And what could we get which would live happily in our tank to eat up some of the new babies as they are born? This way the fry become like live food & we have a more managable tank!
TIA

There's no hard and fast rules, only guidelines. Some say 1 inch of fish per gallon or a certain number per square inch of surface area- these factors are important so it's worth calculating that but there are loads of other things to take into account like the body mass of the fish, type of filtration etc etc.

The best way to tell is to do weekly checks of the nitrAte level just before and after you do a water change. If the nitrAte level rises too quickly in a week then you're probably overstocked. NitrAte should always be below 40ppm but the lower the better (however, if it never goes above zero then you've got a problem). You'll need to check the nitrAte level of your tap water too, it can be shockingly high in some areas. So for example if your nitrAte went from 5ppm to 45 ppm in a week then you've got too many fish (or you're feeding them waaaaaaay too much).

The parents should eat some of the fry, if too many are surviving then you could try not giving them too many hiding places that are too small for the adults too. There aren't many hardwater fish that are compatible with guppies, you're pretty much limited to platys, endlers and more guppies Mollies can be buggers and swordtails get pretty big.

Hope that helps!

Thanks EauRouge!
They do have a lot of plant growth to hide in, so I might take some out and see how it goes. Was hoping to get something a bit bigger though like a solitary angel fish or something...

Angel fish are soft water fish so not compatible really and they are best off in a species tank. They'd get big enough to eat the adult guppies too They have the least appropriate name of any fish, they sure don't act like angels!

The 1" of fish per gallon 'rule' is widely regarded as a load of baloney, if it did have any basis people would be keeping 12" Oscars in 12 gallon tanks.

I'm afraid I also have to disagree with EauRouge's sentiments on the Angelfish. Unless you purchase wild-caught specimens (not recommended) most are captive-bred and are adaptable to a wide pH range. Acidic conditions are favourable if the intention is to breed them.

Well yes, the 1 inch per gallon rule is merely a guideline, I don't think many people would use it to prove you could keep a foot long oscar in a 12 gallon tank.

And as far as I'm concerned, a happy angel is a breeding angel they may survive in hard water but they'll never thrive. Here's a good article on osmoregulation if you're interested.

I concur, I suppose the adaptability of Angelfish in more alkaline conditions depends on certain factors including genetics. However, I would certainly never keep Discus in alkaline water; I've noticed they become more sickly looking and often become more reluctant to feed.

Too true, I would love to keep discus (how cool is their breeding process?! I'd love to have a whole group of little baby discuses nibbling round their mum) but since I'm far too lazy busy to faff about with RO water I stick to fish that are happy with my water.

If you ever need any hints and tips for Discus care, give me a shout. These fish are probably the biggest PITA in fishkeeping, period...