I have the same ruin ornament as you in my wcmm tank !
My nitrite spiking tank is my betta one, I feed him twice a day but he has 2-3 pellets and eats them before they go anywhere so no waste. lol
I used Prime last night to see if it would help stop the huge overnight spike and I am pleased to say it held the level at around 0.10, so no horrid spike when I was not there to control it. It dissipates in 24 hours apparently so I will still be able to see how the levels are going. I highly recommend it for emergency use. I was worried sick about it spiking to 5 again in the 7 hours I would be sleeping, this helped so much. Not adding any more now as I want it to vanish so I can see the levels again. may only use at night to keep fish safe.
When it spiked at 5 I removed the fish and did a 90% change and it dropped to 0.25 straight away, but kept rising hourly from that point and I was doing a 50-70% wc every few hours yesterday. At least the prime gives me and fish some breathing space for a few hours. He will get another large change this morning with my usual dechlorinator so the Prime will dissipate and I can see where I am at. Just hope the spike doesn't last too long. This is stressful and I was knackered last night from all the changes and testing.
Mine seems to be following a weird cycle, I get nitrite spikes of 1.0 every 3-4 days, which one large water change helped, the ammonia drops to 0 at the same time as the spike, then next day the ammonia comes back up and nitrite drops off, did this for about 15 days then I got the big 5.0 spike which wouldn't stop rising after water changes, it lowered but rose fast throughout the day. My snail tank seems to be doing the same thing, while my minnow tank is much slower, been going for weeks, was progressing okay but then I forgot to turn my filter back on after a water change and it was off for about 5 hours before I realised and I think that zapped the bacs, so starting over and about 20 days in from there, but they don't get any large spikes, stays steady in their tank and small daily water changes keep it under control......
Im only in this situation thanks to duff advice from LFS, then I found here and will never do a fish-in cycle again, not fair on me or fish, terrified Im gonna lose them.
Good luck Danny, I'll be watching closely as your in the same situation as me, nice to see another person experiencing the same, makes you feel less alone lol