hardened substrate? cause?
 

I have a spot of substrate that has become as hard as cement (or appears to be) with a little browning of it on the top.

Anyone know what this is or what it means?
All water parameters are quite normal, and nothing jumps out for water quality.

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That happened to me after overdosing alkalinity. It is a precipitation caused from too much alk that somehow bonds the calciferous matter in your subrated together. It can also be caused from too much calcium or magnesium. Each one of these has a balance with the other, if you have too much of one element the excess can form a precipitate.

This is commonly called "Lock Up"
Are you running a reactor? As said in the above post, it could be too much alk and calcium. I've been through this with a friend of mines 90g tank. The entire sand bead locked Up and had to be removed. We then smashed up the solid blocks of argonite sand with a hammer, bring it back to a granular consistency. Terible job... Keep up checking your levels.
Rob

this sounds like bad news. Is there nothing I can do to prevent the rest from "locking up"?

I dont have a reactor as suggested but I do dose calcium via kalkwasser as part of my top off.

calcium is at 410 and alkalinity 9.6

with a alk that low you shouldn't have a problem from that, are you dosing chemicals to maintain alk and ca? if so you might have overdoses and had a percipitation but that only a remote possability. if so the answer would be to add them more oftem to preven having to add large amounts at once.

Steve

I dose kent marine pro buffer DKH a couple times a week.

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Steve, I think you might be confusing Alk with carbonate hardness. Where KH is fine at 9.6, Alk is too high IMO. I try to keep my Alk at about 3.5 Meq/L or 12.25 dKH.

Re: reply
 

nope but you are confusing me now ;) normal peramiter are 2.3 Meq/l or 8dkh, I aim for 12 to 13 dkh for mine also and this is why I am saying with a level of only 9.6dkh or 2.74 Meq/l his alk level is not causing the substrate to lock up.. now what are you trying to say? :mrgreen:

Steve

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Hightower said: What I'm saying is that 9.6 is high Alk. (9.6x3.5=33.6 dKH)

If 9.6 is his dKH than its fine.

Hightower, is 9.6 the measure of your Alk (meq/L) or your carbonate hardness?

I thought alkalinity was usually represented as dKH or meq/L. I don't think I have ever measured carbonate hardness (I thought carbonate hardness mostly pertained to freshwater??).