Thank you all for your advice. I'm going to do a water change and keep doing them over the next few weeks until it gets better.
@AilyNC
Tank size: 110 litres (24 gallons)
pH:
ammonia: 0? tested yesterday at lfs and he said it was good but not sure on value
nitrite:
nitrate: 0? Also tested yesterday but not sure of the actual value
kH:
gH:
tank temp: 25 degrees C, 78 degrees F
I have no idea what the other values are. pH was tested a few months ago at possibly 7.6 but I'll order the API master kit so I can test it. Also not sure on the kH and gH. I get the water from the tap and treat it with water conditioner.
Fish Symptoms (include full description including lesion, color, location, fish behavior): Slow swimming, falling to the floor, not being able to swim straight (spins in circles), rapidly breathing, laying on the sand
Volume and Frequency of water changes: Every 4 weeks, about 15% but I have only done 2 since my lfs said to stop them
Chemical Additives or Media in your tank: Tap water conditioner to any water added, bacteria pearls, about 3 months ago I did a course of anti-fluke & wormer to remove pest snails in my tank (advised from my lfs), a course of anti-white spot & fungus was done about 2 months ago as they were showing symptoms of white spot disease but that cleared within a few days, the recommended dose of aquatic plant food every 2 weeks, the recommended dose of revitaliser tonic about 1 month ago.
Tank inhabitants: 1 cory, 1 zebra pleco, 1 common longfin pleco, 5 swordtails, 3 balloon mollies, 3 endlers, 3 guppies, 4 dwarf gouramis
Recent additions to your tank (living or decoration): 4 dwarf gouramis yesterday, zebra pleco about 1 month ago
Exposure to chemicals: Only the chemicals added which claim to be safe for fish use
@Colin_T I'll attach some photos of the tank and some of the fish but they all look normal. I've got a sponge filter and clean it about every 4 weeks by squeezing it into the water from the tank. It has an air pump attached to it and is on max 24/7. I also have an air stone connected to this air pump which also runs all the time.
I use mains water from the tap and change the temperature to the same temp of the tank each time I add water. I add the recommended dose of tap water conditioner to this before putting it into the tank.
@BoomerXIV I have another 5 litre tank set up but it has 1 betta, 2 female huppies and 1 panda loach in so don't really want to mix these as there's currently no problems with the smaller tank.
Good news: I was looking around the tank double checking for the missing pleco and took apart my sponge filter and the pleco sometimes goes through the middle briefly. Turns out he was hidden (possibly stuck) inside. The filter was only out of the water for about 10 seconds as I was taking it apart so hopefully he will be ok. I have added some revitaliser tonic just to help him but at the moment he is looking happy
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