It’s not been a good week for my fish or plants. I’ve lost two emerald eyespot rasbora that are about 10 weeks old.

Ammonia is between 0.25/0.5. Nitrite was fractionally above zero but noway near 0.25. I don’t know if the fish died due to the spike or the spike killed the fish. Did 75% change.

7 days ago I changed from U3 to U4 filter. 4days ago after 1 fish died so I removed the U2 that was running alongside as thought my juvenile keyhole may have eaten a little fish so put them in my backup.

Fish died Friday and Saturday night. Only found one body. Can a 2cm fish cause a spike like that in a 125 litre? I sifted through the sand and still found nothing, also checked inside the filter so they must have eaten it. Concerned it might have been diseased!

Also my valis plants kind of melted after my keyhole chewed loads of holes in them, little monkey.

Also is this noise normal for a U4? There’s no picture on the video, just sound.

Not going to feed today.

Also can I use Esha optima. Just waiting for new water test results so will post them in a couple of minutes.

Thanks

Just to add there is an extra sponge in the filter one side, I added both sponges from U3, one of which was a u4 sponge, and an extra new u4 sponge. No poly catridge currently.

Test post water change. Against the glass still green but against white it’s yellow

Sorry to read about your fish and plant loss.
Tests usually specify to read against a white background, so I'd say it's closer to 0.
Under the circumstances, I think the water change was sensible. For precautionary purposes, I'd probably advise a 25% water change daily or on alternate days to see if that helps at all, such as to dilute any stress hormones which can't be measured for but may be present in the tank as a consequence of some fish fatalities.
The fish filter change sounds like it was done correctly. I haven't time to check back to your previous posts to see when you added the second filter or if it was always there. However, if you add a new filter, then it's best to distribute the mature filter media between the two filters so that both are 'colonised', otherwise the newly added filter may not actually develop any beneficial bacteria in it. It's (also) possible that the loss of any beneficial bacteria on the U3's hard surfaces, plus the loss of the U2, may contribute a little to an ammonia rise.
Another place worth looking for a body is around the suction cups, behind the filter or in the filter bracket itself if one exists - I've found a few fish bizarrely squeezed in those locations and behind/under rocks, with the body only appearing once the decor is completely removed rather than simply nudged.
If a filter is noisy, then I've usually managed to rectify it by taking it out, ensuring no grain of sand is around the impellor, turned it upside down in the water to release any trapped air, and made sure the cable is not vibrating against the glass.
eSHa Optima ought to be fine to use.

Thanks, I’ve been doing daily water changes at 25% and nothing has changed.

I’ve moved fish around a bit now but don’t want to risk crashing the cycle in the other tank so in the main tank now there are:

4 x honey gourami full size
9 x 2cm ish emerald eyespot rasbora
6 x celebes rainbows 4-5ccm
1 x platy full size

Do products like Seachem Stability actually help or do they just stop the cycle doing what it needs to?

Thanks