Quick question about water temps

[ButWhyIsTheGinGone]

Hello all,
I have had a big 300 litre cold water tank for just under a year now and I love it. However, due to my naivite (and PaH's general crapness) when I started out, I bought six beautiful platys to go in it. I now realise these need warmer temperatures to survive. I have kept an eye on them until now and they have seemed fine, very active.
Now, however, it's obviously a lot colder than when I bought them, and some of them are seeming very still and are hiding up by the filter. I feel really bad about this.
I look after a few other tanks, both at home and work, but none have the capactiy at the moment for 6 extra fish. So, I was thinking. The 300 litre tank came with a 100w heater and I've never used it before. Can I turn it to about 74 to keep the tank at a decent temperature? I keep my house very cold so unfortunately the water stays cold.
I'm only asking as I have 2 black moors in there (soon off to my friend's pond) and also my beloved weather loaches and some minnows. I obviously don;t want to hurt them in any way. I am willing to take the platys back if necessary, but could anyone tell me if this is a do-able solution?
Thanks x

There is a cold water platy, I think they're called variatus (?) they tend to have a yellowish body, orange tail and have horizontal stripes along their sides. Even though these are cold water fish it may be the cold that's slowing them down while it's really cold.
I don't know how how warm you could get a 300l tank with a 100w heater but you wouldn't want to make it too warm anyway because of the moores.
Might be worth warming the tank a little and keeping an eye on how they're doing.

Hi Snowfire,
I think all Platys are variatus something but I'm not sure. None of mine have any stripes but I did get them from the "temperate" tank in Pets at Home.
Anyway, I decided to put the heater onto the lowest temperature, despite it being a tiny little thing! The temperature has crept up to 62 degrees and it seems to be having a good effect. The platys certainly seem more lively, as do the danios...

Good news! I think even cold water fish like a little warmth. I know my pond fish are looking a bit slow and depressed lately. No way I'm going to try to heat the pond though
I think P@H will tell you anything if it means a sale!

I've never heard of variatus being coldwater fish, they just need the same conditions as other platys. They are tough fish and can tolerate lower temperatures but they should be kept at around 23/24C to keep them at their healthiest. A lot of 'coldwater' fish that you see in aquatic stores are actually from temperate regions and may need heated tanks if your house gets cold at night. I wouldn't say they were compatible with your other fish unfortunately.

BTW, black moors are not suited to ponds, they are too delicate and they can't swim fast enough to evade predators. Are you trying to rehome them?

I think the moors are in the 300l tank with the platies, assuming they aren't overstocked and the temp can be maintained (aqadvisor recommends 18-25 for platies) that would be ok wouldn't it?

Hmm, not sure. Platys can be buggers. They are also happiest at a temperature that is too warm for the goldies. Fancy goldfish are best off in a species tank IMO because of their delicate fins and they are crap swimmers so the other fish can usually out-compete them for food.

Yes I'm trying to re-house the moors. They are the first fish I ever got and I really want them to be in a good environment. I thought they would be ok in a pond - oh dear! They are about 3 inches long and brilliant but I don;t know anyone who can take them. Don't really want to give them to PaH as you don't know where they'll end up.

The tank temp seems to have settled at 68 and I have to say all the fish are really looking a lot perkier for it. I know it's not ideal for the platys but they do seem a lot happier for the mean time.