Yeah it was in a packet. Going to do a flush as soon as possible, I’m going to put the wood in some boiled water to see if that’ll let me salvage it
Did you buy this packet from Amazon, sold as "aquarium plants" or "carpeting plants" fairly cheap? I've heard of these things, and they're a risky scam. Often the seeds are of a none aquatic plant that will grow for a while, then die off, potentially spiking ammonia as the plant matter decays.
Most hobbyists aren't growing plants from seeds. We buy a rooted plant, stem cuttings, in-vitro grown young plants - things like that. Planting any kind of seeds in an aquarium isn't usual, and it's likely a dodgy scam where they send you any old seeds, even normal grass seed! As pointed out, they may well be coated in pesticides, fungacides etc.
Look up "aquatic plant seed scam" and see for yourself.
It's easily done. On impulse I bought some cheap Chinese root tabs capsules once. Thin clear capsules containing dozens of little bright yellow balls. I added five capsules underneath my root feeding plants. Within days, the capsules had dissolved. They quickly fell apart in the sand and released way too much of something unknown into the water. Luckily my fish were not poisoned, but it lead to very high nitrite spikes despite 75% daily water changes, even twice daily to try to save my fish and get the nitrite down, while sifting through the sand to remove so many of these random yellow balls of "plant fertiliser" which could have easily wiped out my whole tank if I hadn't tested the water and done the huge water changes.
Aquariums are fragile, and while cheap deals are tempting, I've regretted more than once getting something from a dodgy source, Could have been anything in those yellow balls. I won't ever add something to a tank now unless I trust the source and know what it is I'm adding. It took weeks to stablise that tank again, and I lost a guppy to the high nitrate.
I second/third/fourth the suggestions to strip the tank and start over. I wouldn't trust the wood piece, but might try cleaning it/boiling etc and try it once, maybe in a quarantine tank first to see if the fungus regrows and whether it's poisonous. Since these seeds are scattered in the substrate, I'd bin that and get new substrate too.