Urgent Help Needed With Established Pond

Our pond has been up and running for a while now (few years) without problems. it consists of a few parts....a black rubbermaid tub (filled with plants) which flows into a bath (filled with plants), which flows into the main pond (made from pond liner with a few plants in) on the other side is a large aluminium 'pond' (filled with plants) which flows into the main pond via 2 waterfalls. The fish (a few goldfish and 3 very young koi) live in the main section. The pond is a bit over 3000L .
 
we've had a bit of an algae problem this year which we are combating via a biological powder you add to the water (no chemicals) we have also just last week installed a uv steriliser.
 
the last few days the algae has really started to die back and a thick green 'scum' has been floating on the surface of the main pond. (mixed in with white frothy slimey bubbles) we've been scooping this out but it seems to reappear just as fast. 2 days back we noticed all the baby fish (born this year/last year) were covered in a white slimey film and/or white spots. we've removed these from the pond and have them in quarantine inside (treating with esha2000 and esha exit)
today i came back from work and the bigger fish were gasping at the surface the entire surface covered in the green/white frothy slime. i threw in a few extra air pumps and got scooping at the surface removing as much as possible of the slime. after a few hours the fish seemed to be swimming normally and no longer gasping. I did a water test using an api liquid test kit. i was shocked at the results but im not sure if they make sense? nitrate 0 nitrite 0 ammonia 8+?? how can i have such a high ammonia but no nitrite? also ph seems rather high 8.4 but this was taken at 4pm in the afternoon. ive half emptied the pond andam refilling wih water from the rainwater barrels and the stream by the house (our usual water sources) i'll be doing another water test within 30 mins when the pond is filled back to its usual level. i'm looking for advice on what to do next. i know ive got to get that ammonia down but am confused at thehigh level but not showing any nitrites?  what is causing the slime? is that the algae dying off? would that cause the ammonia levels? are my fish doomed after being in such high levels? i dont want to shock them by changing too much water too quickly....
ive tried adding a photo but get the message that its too big to uploa here.....

Yes, it'll be the algae dying off that's caused the both the slime and the ammonia spike. It's probably too soon to see raised nitrite levels, but that'll probably come
 
I know you're worried about shocking the fish, but they will be in a bad way if they stay in the level of ammonia; it prevents them absorbing oxygen through their gills, which is why they were gasping at the surface.
 
All you can do is continue to change as much water as possible until things get back to normal.
 
Best of luck; I'll be keeping my fingers crossed for you!

hi a little update on the situation and am looking for some more advice. its been 18 days since i last posted....
we stopped the uv filter and didnt add anymore powder for the algae. we've been doing lots of water changes and did a really big one a few days back (emptied about 50% of the water out, scraped the bottom of the pond for debris and scraped off remainder of dead algae.
 
been doing daily test and am a little suprised by the ph results.
we're back to reading 0 ammonia 0 nitrites and a small reading for nitrates. (around 5-10?)
this was measured seperatly in each filter part and the main pond (we had turned off the main pumps to stop the water flowing from one filter to the next and gave each filter section their own pump...so really its now 4 seperate pond parts)
 
the black rubber maid tub (with plants) PH reads at 6.2
the bath (with plants) reads at 6.4   both of these filter parts seem to have a heavy infestation of some sort of bugs? they look like tiny shrimpy flea like things..there are so many appearing it looks like the water is 'alive' and wriggling.
 
the big aluminium section (with plants and fish) PH reads at 8.0
the main pond (with plants and fish) is reading at 8.2 now
 
 
where do we go from here? is it safe to turn on the main pumps again to let the water flow through each part with all the different PH values?
any idea to the cause of the vast difference in ph values? (all water for changes is taken from the same source...the ph value of the source is 7.0 - 7.2 depending which time of day we take it)
 
any help greatly appreciated

I'm struggling slightly to understand what you've got going on with the different containers, but I think I've got it.
 
I suspect that flutter was right with the initial diagnosis and, not matter what you do, some dying algae will remain. Various pond critters will love this and will multiply rapidly. Once the pumps are back on the fish will make light work of them.
 
Generally, a rising pH to me suggests a lime source. Possibly in run off from the soil around the pond.
 
I'd probably turn things back on again and get back to where things were.

hi thanks for your reply.....ive been trying to upload a photo so you can see the set up but its not working. it says the file is too big? how do i change this please?
ive fished out another 2 sick fish today they have a weird 'slime' covering over them and red sore looking areas. should i be treating the pond with an anti fungal or is this perhaps from ammonia burns from when the ammonia was high?
no soil can run into the pond as it has raised edges all the way round...

photo 1

photo 2

Spishkey said:

hi thanks for your reply.....ive been trying to upload a photo so you can see the set up but its not working. it says the file is too big? how do i change this please?
ive fished out another 2 sick fish today they have a weird 'slime' covering over them and red sore looking areas. should i be treating the pond with an anti fungal or is this perhaps from ammonia burns from when the ammonia was high?
no soil can run into the pond as it has raised edges all the way round...

photo 1

photo 2

Click to expand...

 
What items do you have in each segment of your pond? You need to identify these items and look to see what effect they have on the PH values of the water.
 
A PH value of 6.5, which you mentioned above, is on the low side for goldfish, shubunki, rudd, koi, orfe. They require a PH of between 7.2 and 8.2.
 
With regards to the sores, both alkalinosis (a heavily unsuitable alkaline PH) can cause burns/sores and the ammonia level you recorded will definitely have caused severe skin reactions. A PH of 8.8 would be sufficient to cause skin problems and ammonia levels above 0.2 ppm can cause skin problems. 
 
One question, are you using aquatic soil or regular garden soil? You should be using the former as garden soils can have either very high/low PH levels.