Why Does My Platy Have A Red Belly?

Phew!....that's a relief...I thought for a moment we were gonna get some sort of fish porn...or at the very least, platies with censored bits

Sort of 'Fifty Shades of Grayling'?

Sort of 'Fifty Shades of Grayling'?

...groan...what are you like?

I'm going to ask about a sensible heater for the biorb on Saturday but now I have another question - will the platies who have been used to room temperature find it too warm if I take the temperature up to 25 degrees or so? And if I do that and they're all happy, can I put a couple of little tropical fish in there with them? Or should I just get a few more danios so my lonely little survivor can shoal with them?

Platies will be fine at 25ºC.... just make sure you increase the temperature slowly.... 1º per day sort of thing.

Is there any reason you want the tank at 25ºC? I run mine at 22º and everybody's happy.

I was reading on Amazon about a man who was trying to heat his 60ltre biorb to 25 degrees and the heater couldn't cope. Another man said his fish had been cooked in the baby biorb so I guess I had 25 degrees in my mind.  My house is kept warmer than most day and night as it holds it's heat really well and I hardly ever need to use the central heating overnight.

I might just wait until autumn then buy the heater but keep it at 22 - the heater should be able to handle that surely!

Am really embarrassed as I was looking at completely the wrong part of the fish to see what sex they were - I was looking for another fin/pole at the end of the tail!! Now I can see easily what I have - and guess what.....red belly is a boy 

So the original question has now been answered - it's just his coloring. How funny is that? Thanks for the educational picture ColinB.

Susie, there are tales of people's fish being cooked. Heaters can fail in one of two ways - they can stop working altogether, in which the water gets cold; or they can stick in the on position so the water gets too hot.
Most heaters have a thermostat which turns the heater off when the water reaches the set temperature (except when they fail in the on position) but they are usually badly calibrated, meaning that although you might set it to 22 deg it could turn off at anything between 17 and 27 deg. The way to set a heater is to set it low and turn it up 1 deg on the dial every few hours and measure the actual temp of the water with an internal thermometer. When the thermometer shows the temp you want, that is the heater setting you want regardless of what the dial says.
I say an internal thermometer as those that stick on the outside don't give an accurate reading of the water temp.



At least you know what sex your platies are now. Do you have any females at all or just males?

Hi FC - nice to meet you too
I know what you mean about the platies chasing and pecking - red belly is a total thug! I thought he was a pregnant female at first but he's just big, fat and bossy. He's currently stalking pale skin (female - the one with the red spot on her face) Now that you mention it, I wonder if the red mark on her face was where she's scratched herself on an ornament trying to get away from him (Sue - the mark is going down now and she's very active so glad I watched and waited).

I know what you mean about ammonia levels - I overstocked my tank before it had cycled and paid the price for it (lost 4 danios and 5 ghost shrimp in a week) Lesson learned for both of us I guess? I really want to get some more danios as I only have 1 left now and he's looking really lost and lonely. But I'm not going to do it until my tank (stupid biorb) has cycled properly
Sue - ammonia still at 0.25ppm but nitrites/nitrates both nil - isn't the ammonia supposed to turn into nitrates then nitrites? I'll do another 25% water change tomorrow and see what happens.

FC - The only bit of advice I feel qualified to give you is to listen to Sue...she had me totally freaked with her massive water change recommendations. But she was right all along, the levels only started to go down when I took her advice and did a massive water change.  Have your 2 platies got a 54 ltre tank all to themselves or do you have other fish in there too? The pet shop told me that they prefer cool (but not cold) water so maybe you're right, maybe it is a bit warm for them at 24 degrees?

Sue - the 3 gold colored platies are all males. Then I have the 4 'speckled' platies. 2 are male and 2 female. For some reason the gold colored ones don't bother the ladies as much as red belly and 2 spots (both speckled) do. Do you think they recognise that they're different - or is it just that they don't get a look in? They seem quite happy swimming around in their own little trio. And I've decided to wait until the autumn to get a heater - then get a good one and aim for a constant 22 degrees

Ain't fish fun 

Oh, and dbaggie - thanks for rubbing it in but you're correct, that is where I was looking  what a muppet I am!

Apologies  wasn't trying to rub it in, quite the opposite actually - just showing how easy it is to get mixed up with fish anatomy!

ammonia still at 0.25ppm but nitrites/nitrates both nil - isn't the ammonia supposed to turn into nitrates then nitrites? I'll do another 25% water change tomorrow and see what happens.

Ammonia -> nitrite -> nitrate

When you have enough bacteria and are doing weekly water changes, there should be no ammonia or nitrite but nitrate will build up. One of the reasons for doing water changes is to remove the nitrate.
With a fish-in cycle, you start with no bacteria. Ammonia is excreted by the fish and builds up, that's why you have to do water changes to keep it low. Slowly ammonia eating bacteria grow and they convert ammonia into nitrite, so as these bacteria grow nitrite starts to build up so you need to water changes to keep that low as well. Once there is nitrite, the nitrite eating bacteria can start to grow and they convert nitrite into nitrate.
It takes a long time for enough of both types of bacteria to grow, and the nitrite eaters can't even start until the ammonia eaters have made some nitrite for them to eat. It does sound wrong doing water changes to remove ammonia and nitrite but even a trace more than the current number of bacteria can eat will stimulate them to multiply. Eventually you will have just the right number of bacteria to eat the ammonia made by the fish and the nitrite made from that ammonia.

Re your tests:
0.25ppm ammonia could be a false reading as some people never see the yellow colour of zero. As long as that doesn't go over the 0.25 colour, I'd regard that as being zero.
Nitrite is easier to see the zero colour. With the API test if it is blue it's zero; if there's a hint of purple, it's not. With several fish in your tank if there weren't enough ammonia eaters I would expect to see your ammonia reading a lot higher than 0.25. Since you obviously have a fair number of them, they will be making nitrite. And again, if you didn't have enough nitrite eaters I would expect to see a reading for nitrite.
Nitrate is trickier. That should go up if you have both types of bacteria growing. And it is very unusual in the UK for there to be zero nitrate in tapwater. And you did report nitrate of 40 in the biorb in your earlier posts
Have you tested your tapwater for nitrate? Unless you have a heavily planted tank, you can't get the tank nitrate lower than the tap level by doing water changes with just plain tapwater (plants use nitrate as fertiliser which is why it can be lower if you have a lot of plants).
And just to check - you are shaking one of the reagent bottles, the instructions will say which one. All makes of tester have a reagent bottle with a chemical that settles out on the bottom. the shaking is necessary to redissolve it.


You have 7 platies, 5 male and 2 female? Unfortunately that is not a good combination. The recommendation is to have twice as many females as males as males will harass females and with more females each one gets time off while they chase another. Yours are probably quite young at the moment, but as Colin says once they reach puberty, things could change.

If you got more platies, you'd need rather a lot of females. For 5 males, you'd need 10 females, that's another 8, and 15 platies is somewhat overstocking a 60 litre biorb. One option would be to rehome the two girls.

Danios actually need quite a big tank as they are very fast swimmers. A lot of people say 4 ft is the minimum tank length. I would not keep them in a small tank like 25 litres. I would seriously think about rehoming the one you have rather than get more.

Or you could give the biorb to your daughter......


Given your ammonia and nitrite, I would say you are cycled if it wasn't for the nitrate. What is the level in your tapwater?

It's the fact that the nitrate is nil that's worrying me. It is virtually unheard of to have zero nitrate in a tank that is cycled. In almost every case where nitrate is zero, the tank is NOT cycled.
Nitrate is the last stage in the nitrogen cycle, and as there are no bacteria to remove it in the typical tank, it builds up and we have to do weekly water changes to remove it. There are bacteria that eat nitrate but they don't grow under typical tank conditions.

If you mean nitrite is zero and you have a reading above zero for nitrate, that is what I would expect.