Nitrate!

[allgipan]

Hi, I have recently added 3 male and 2 female guppies to my tank, should have had a quarantine tank but you live and learn. Within 24 hours both females turned black, flipped over and died. One of the males is not eating now and 2 of my other fish are flicking and being slightly aggresive. Below are my stats and the Nitrate is concerning me, its too high yet I do a water change every week of 20% and did one last night too, I also hoover my sand regularly aswell as cleaning the ornaments and maintaining the plants.
The tank has high levels of algae and i have snails too. Stats are below!

96 Litre tank,
Temperature 25
PH 7.8, difficult to alter in my area as tap water is 7.6
Nitrate 80 ppm
Nitrite 0
Ammonia 0
Fish, 1 Dwarf Gourami, 2 corys, 3 tetras, 5 zebra danios, 1, 3 inch sydontis, 3 guppys....maybe 2!?

I was confused though as my nitrite and ammonia are good? I have recently put the ammonia and carbon filter back in as I had algae med in, last meds in were anti internal bacteria 3 weeks back due to fin rot on one tetra which since died.

Any help appreciated, just hope I have not done something totally dumb xxxxxxx

 

[WILDER]

The females did they turn black completely all over or just black patches,
What is your tap nitrate reading.
How long has the tank been set up.
When did you last touch your filter sponges.

 

[allgipan]

The females did they turn black completely all over or just black patches,
What is your tap nitrate reading.
How long has the tank been set up.
When did you last touch your filter sponges.

Hi Wilder and thanks for your time responding,

Tap nitrate is 40,
Tank been set up for a year and a half
The girls were a light blue to white and turned to a mid grey all over the body, tail was red naturally so didnt spot the colour change there so much
Filters not been touched for 2 months at least, I generally clean them in tank water removed when doing water change but they do get slimed up with algae.

thanks xxxxxxxxxxxxxxxxx

 

[WILDER]

If you have a tap reading of nitrate at 40 that means you can get your tank nitrate reading lower.
I would just slighty rinse one of your filter sponges in old tank water if its really mucked up.
How long did you climatise the guppys for, was there any excess mucas on the fish.
Grey white patches can be columnaris to parasites.

 

[allgipan]

If you have a tap reading of nitrate at 40 that means you can get your tank nitrate reading lower.
I would just slighty rinse one of your filter sponges in old tank water if its really mucked up.
How long did you climatise the guppys for, was there any excess mucas on the fish.
Grey white patches can be columnaris to parasites.

Hi,

I aclimatised them for half an hour, they did appear slightly chalky, not little spots but matt and not shiny like my other fish.

The grey was definitely under the skin, not like a lesion or area xxxxxx

 

[WILDER]

Ok.
Any of your fish that are left showing signs of flicking and rubbing against objects in the tank.