Never had trouble with pH before, but never had to deal with RO water, either. Apparently the little bit of gravel, maybe 1/2 pound, I added as decor is the prime suspect in the jump of my pH from 6.6 to 8.4. Most of it sealed off with the silicone I used to attach it and whatever coating TopFin uses to make it shiny. You can see all of the gravel from this angle. It is a single layer siliconed onto french drain piping
The KH has gone from 6 dKH to 7 dKH, not enough to matter to me. Would so little gravel cause this shift? The only other change is the addition of plants but that should bring it down if anything, right? I can remove the gravel (substrate is EcoComplete) and redo the work with trap rock which, from what I am reading, is basalt and doesn't mess with the pH if the gravel I used is the culprit here. Your thoughts?
It's possible for the gravel to have raised the PH. Did you test PH the same way both times too? PH can be a very finicky thing to test because it is effected by gases in the water too. Are you keeping soft water species? 8.4 isn't really a big deal unless you intentionally want your PH to be lower for a specific species.
Thanks. I want to keep clown loaches and rummy nose tetras as well as my blue gouramis who really are fine with this pH. The pH was HIGHER at the pet shop, actually. Before I added the decor with the gravel, the pH was holding steady between 6.6 and 6.8.
I found a source for trap rock nearby and I figure I can use that and do some snow highlights in perlite. I am planning on just redoing everything from scratch, then, once it is cured, swap out the loach lounges. The fish are getting used to me mucking about in there since they keep digging up my crypt parva. Grrrrrr. That stuff is expensive!
Calcium carbonate rock comes in many forms and does produce a high (above 8) pH in the aquarium.
From Wikiedia: Calcium carbonate occurs as aragonite, calcite and dolomite. The carbonate minerals form the rock types: limestone, chalk, marble, travertine, tufa, and others.
In fact both aragonite and dolomite are both sold in bags in pet stores as a substrate for use in aquariums designed to keep Rift Lake aquariums at a pH above 8. It works well. I use either cacium carbonate rocks or crushed limestone to keep tanks for both my livebearers (swords, platys, variatus, and guppies) and and some Rift lake species (labs, demasoni, petricola) at high pH.
One easy test for carbonate rock in any form is to drop a few drops of Muratic acid (HCl acid) on it and see if it fizzes producing CO2.
Yup. I have 40% acetic available and it fizzed in that, too. It just never occurred to me that something intended for aquaria would be so reactive. What were they thinking? I am probably paying more attention now that I am fooling with RO water. Ignorance (and city water) is bliss. I also wasn't using this decorative gravel before, either. I am rebuilding my loach lounges using trap rock and perlite. Picked up the trap rock at the landscape company today - they had to use a backhoe to get the snow off of it for me. We got a foot of that white stuff yesterday. Once I am ready to swap them out, I will start the process of lowering the pH. Good thing the fish were in slightly more alkaline water at the shop so bringing them home wasn't such a shock.
I have removed the decor that was covered with the offending gravel, drained 1/3 of the water (I want to keep the heaters covered, it IS winter in Minnesota, afterall) and took the following measurements:
TDS 123
KH 7
pH 8.0
The remaining water was about 80 gallons.
I added over the course of the day about 15 gallons of RO water measuring: TDS 5
KH 2
pH 6.6 The pH hasn't budged. The raw well water (filtered, not softened but Fe removed) is pretty much perfect except for the high KH, though. Is there a way to lower just the KH? TDS 209
KH 21
pH 7.2
Thank God for my hardy blue gouramis who are just going with all of this stuff and who finally recognize me as the food lady.