Putting nutrients back into Multi-Purpose Compost

I was wondering what people do to put the nutrients back into the compost after a season. I've been doing a little looking into it and see people have been using Epsom Salts.

I have Magnesium Sulfate, Bicarbonate of soda, Lugols Iodine I use for other things and wondered if other people use them, or other 'chemicals' to put nutrients back into the compost for next season? I know I can use Magnesium Sulfate as that's what is in Epsom Salts, it's just I don't know exactly how much to use as the results I've found are mainly from America and they're different to our amounts and I don't how to convert them.

I was also wondering what people think about this idea...
I am growing tomato and have a bottle of tomato food. I was thinking about mixing the full bottle with the appropriate amount of water and after collecting the compost back up, a full bag of 125 Litres worth (a B&Q bag) and pouting the whole bottle worth of diluted tomato food into the compost to put nutrients back into the compost. To use with everything I'm growing, not just tomato.

 

Sounds a bit like a chemical nightmare to me
Will be difficult to work out what and how much to add of any one chemical.
Magnesium is only a trace element as far as I know, and required in fairly low proportions compared to the three main feeds of nitrogen, phosphorus and potash.

Not come across bicarb or iodine in plant growth myself but I'm sure they might fit in somewhere.

Think I'd be inclined to add, an amount of Fish Blood and Bone , and go with that.
But how much is going to be open to debate I think.

 

@pooky2483 I don't reuse MPC it gets tipped into the veg plot. I tend to grow most things in a mix of MPC and garden soil. Depending on the MPC you buy there is only a few weeks worth of nutrients in them hence the advice to start feeding when the first truss of flowers opens.
When bought the MPC contains a balance of N, P and K plus some trace minerals. More expensive MPCs have slow release fertiliser pellets in them (green, blue pellets) and claim to feed for the whole season. Soluble fertilisers like Miraclegro and Phostrogen contain N.P and K plus the necessary trace elements.
If you really want to recycle I would go with Pete's suggestion of blood, fish and bone, however disease build up could be an issue.
Lugol's iodine is a disinfectant, Sodium bicarbonate is an antacid and will make the MPC more alkaline and as Pete said magnesium is a trace element.
You can buy the slow release pellets, but I have no idea how much you would need to add.
If you want to give it a go then you should be able to find recipes online and stick to UK sites to avoid conversion issues. A final thought would be that everything will need mixing really thoroughly and try and avoid adding liquids at this stage as they will mainly run through and may take other nutrients with them.

 

The reason I asked was that when we eventually get the garden sorted... Slabbed and a shed & greenhouse & small raised bed for the OH, we wont have access to soil.
So it looks like I will have to buy some soil from somewhere to replace the MPC.

Thanks to you all for your advice and I only asked if the stuff I had could be put to any use in the garden as I have an abundance of them.