Reef nutrition

Keep an eye on your DI resin!

I know quite a few watch BRS videos around here, but for those that don't

Synopsis/spoiler of video (if you don't have time/desire to watch)
Deionizing resins attach at a molecular level the stuff that gets buy the RO membrane, ammonia, silica, phosphate, nitrate, etc. However the strength of the bond depends upon what the element is, e.g. silica has a much weaker bond than phosphate.

A simplified view is that these elements bond with the first DI resin it comes across making that resin "used", however if something with a stronger affinity (attraction) comes along it will knock off the element with a weaker affinity replacing it. Normally this isn't a problem as that element with a weaker affinity just binds with the next DI resin it comes across, and this process continues as you go through resin. However when the resin is all "used up", it doesn't mean that it doesn't work anymore as elements with stronger affinity will still be absorbed but at the expense of knocking off the weaker affinity elements off the resin except now there's no more resin for those weaker affinity elements to bind to and it just starts kicking them into your RO water container, net result is you get a spike in these weaker affinity elements. Even worse is that this migration of weaker affinity elements (e.g. silica and ammonia) starts before the DI resin is used up, so if you're like me who wants to make sure every last bead changes color because "damnit that stuff ain't cheap" then you will start to "soil" your "pure" water.

Solutions to this is to double up on resin bays, that way you can run one to absolute exhaustion and the second one will pick up the slack of what gets through near the end, then swap out your second one into the first spot, and put brand new stuff in the second spot. Or you can simply deal with the elevated silica/ammonia in your RO water because you'd rather have that than nitrate/phosphate :)
 
Ok, I just watched it. Towards the end of having my tank up I was showing 1-2 tds getting through my di but I didn’t address it since I figured it was only 1-2 per million. Looks like I was letting ammonia and silica through.
 
Yeah, I have had no desire to replace my DI resin because I figure "WTF it's the (longest in the history of reefing) temporary storage tank for fish only, the water doesn't need to be pristine" plus it's literally only top off water at this point. But at this point I've run with exhausted DI resin for so long I'm sure all the ammonia/silica is already pushed through :D
 
Sort of related topic......and hopefully for benefit for those club members who read sfsuphysics post above...
The same molecular bonding properties that affect DI resin happens with activated carbon. Hence the reason why it might be counter productive to leave AC it in for long periods of time
 
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