Odd Platy Behaviour- Ideas?

[missPenguin]

Two of my red wagtail platys are beahving very oddly. They are just restling listlessly on the bottom of tank, not especially moving that much much. Earlier all were fine then one started to hide behind the filter just hovering motionlessly at the surface. They do not appear to be gulping for air and thier fins are upright and proud as usual.

The tank is reasonably heavily planted running with 2 fluval 3 plys filters and an airstone

Water stats are

Ammonia 0ppm
Nitrite 0pmm
Nitrate 10ppm
PH 7.2
GH 1.25 english degrees
KH 3.75 english degrees

The above results are typical readings for my tank, I haven'yt had any kind of ammonia or other spike for weeks now [touch wood]

The water is changed weekly, in fact I have did a water change yesterday because we were fitting the filters with spray bars [which is the only change I've made recently] and as a precaution I have changed 20% after the odd behaviour started tonight.

All 3 females have given birth within the last 10 days

I'm completely puzzled.

By comparason, the panda corys couldn't be happier and the male platy is absolutely fine.
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Fluval Duo Deep 800 126 litre

3 x red wagtail platys [f]
1 x blue mickey mouse platy [m]
1 x mini platy [6 others gone to new home ]
5 x teeny fry
2 x panda corydoras
2 unknown snails

Quarentine Tank- 5 Gallon

2 x croaking gouramis

 

[Tokis-Phoenix]

How many male and female platies do you have? Are the odd platies eating and what gender are they?

 

[missPenguin]

How many male and female platies do you have? Are the odd platies eating and what gender are they?

I have the 3 females to 1 male ratio as suggested. They are eating but they are not exactly going nuts for the food when I put it in like they normally do. The 'odd' platies are female, all 3 of the females have given birth within the last 10 days but only two seem to be exhibiting this behaviour.

I've checked the tank this morning and all the fish are swimming about happily but it's hardly a hive of activity as it usually is.