Red line torpedo barb sudden death

[rob_w]

Hello
I'm wondering if some one can help me explain the death of my red line,or mainly explain the bruise.
The tank is 450L ,I have 2 fluVal 306 external filters
Tank temp 26,degrees C
Ammonia -0
Nitrite-0
Nitrate 15
PH normally 6.8/7

I use RODI water mixed 50/50 with tap water (treated and mixed with tropic Martin pro discuss mineral)

The tank is planted with And I inject Co2 .

I have

10 angelfish
4 Bolivian rams
5 panda Cory's
5 sterbai Cory's
5 bronze Cory's
1 knife fish
10 cherry barbs
1 ancistrus pleco
2 cockatoo fish with 3 femails
3 torpedo barbs was 4

I had a PH crash down to 6 or 5.8 and I alerted by this with the torpedo barb having elevated gill movement but swimming round normally.it was to late to do a water change so was planning to do one first thing in the morning .
In the morning I noticed the barb had died was gutted.
Iv attached a photo of the fish as when I removed it from the tank I noticed a bruise on its belly and was wondering if anyone has seen this before. Was it the ph crash or is this I sign of something totally different . Thanks guys

 

[Delapool]

I'm going to go with the ph crash causing it.

 

[tanz8anz]

My swordtails looked like that when my ph dropped below 6 which actually wiped out my entire tank but my swordtails looked just like that wen i got them out if the tank

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[rob_w]

Thanks for that,the bruise was worrying me thinking it was something else.
Iv put some coral sand in my filters and after a lot of testing I have got my ph swings from 6.5 at night and 7 in the morning so I'm pleased with that ,and angel fish are all laying eggs every week so they must be quite happy

 

[tanz8anz]

The angels will love the lower ph water

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[rob_w]

Is it possible to load videos on here ?

 

[tanz8anz]

Should b able to ive seen people add videos some have put them on youtube and attached the link.to the forum

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[rob_w]

Cool will have to look into it got a video of the angels spawning 2hours ago !!!

 

[tanz8anz]

Oh nice that would be cool to c

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[rob_w]

I'm just uploading them now and I'll post the links here

 

[rob_w]

 

[rob_w]

 

[tanz8anz]

Ooo wow.that is amazing i love the colour of ur angels ive got a beautiful greeny bronzy stripped angel with eyes it is my favourite..

When i was feedng my fsh this morning i saw a little face pop out of an.ordament and i thought it was one of my clown louches but then.realised they were all out eating and my next thought was my male kirbensis but no he was out eatng all fish were accounted for so im.not sure who this littpe face was

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