What do you add to your tank after a water change?

[AbbeysDad]

How often do you add Iron if you have plants?

Never

Is there any benefit in adding Seachem flourish excel after a water change?

Excel is made from glutaraldehyde, a chemical used to STERILIZE heat sensitive medical and dental equipment. It kills algae and some plants and can't be good for fish!

do you add any ferts for the plants?

Yes. I'm using Greg Sage's (selectaquatics.com) Rapid Grow fertilizer along with a little Seachem Flourish Comprehensive.
I have a 3-4" layer of pool filter sand in my 60g (untouched for 8+ years), so for the Amazon Swords I use Flourish root tabs here and there (they are heavy root feeders). Note: there are Malaysian Trumpet Snails that burrow in the sand.
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I have Seachem Safe on hand in the event of an unforeseen ammonia spike, but I'm on a well so don't have chlorine or chloramine to worry about.
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I do have nitrates in my well water so I do pre-filter much (but not all) of the water I use for water changes (see My Nitrate Fight).
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On the 60g, I'm experimenting with a DIY anoxic filter. On the 40g sump for the 110g stock tank, I have two BCB baskets that I recently redid (see Take 2: Anoxic Clarification Baskets)