TDS >350 Substrate Mistake(s)? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 09-05-2020, 02:00 PM Thread Starter
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TDS >350 Substrate Mistake(s)?

I live in Austin, TX, and our tap water is hard, TDS about 150 according to my simple dip meter. I've had my 90-gallon tank filled for about five days and I've been slowly siphoning out water and replacing it with RO/DI water (all new filter cartridges) that measures about 15 on the same meter. I've replaced maybe 15% so far. I have some swords and a few other plants planted with Seachem fert tabs and a little Excel and Stabilizer and so forth. Nothing exotic, everything conservatively dosed, for example the Excel is limited to 1/5 of the directed dosage.

I've been waiting for the nitrogen cycle to do its thing, but ammonia is remaining at 0.5 mg/L, with about 12 mosquitofish enjoying their new digs after being in a tiny "pond." For a while I had a bunch of pond plants floating in the tank, so I suspect/hope my tank is more cycled than I had first suspected. A nitrite and nitrate test is in the mail.

I hadn't bothered to check the tank water for hardness until last night when I was absolutely gobsmacked by a 350 reading! WTH? Today I will begin a major water change, perhaps >75% over the next two days. But now I need some knowledge and guidance. The substrate is thin and a little haphazard: two 7kg bags of Seachem Flourite, maybe 30 pounds of pea gravel, 40 pounds of playground sand, and two medium-sized rocks that I believe are not sedimentary in nature. I also have about 40 pounds of so-called "egg rock" from Lowes. I have another 14 kg of Flourite coming in later today. Which of these is most likely the water-hardening culprit?

Thanks for your help and expertise!
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post #2 of 4 (permalink) Old 09-05-2020, 04:45 PM
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It's almost bound to be your rocks. Fill two buckets with RO water and place rocks in one for 24 hours, then test each. If the TDS is higher in the bucket with rocks, you'll know they are the culprit. Offhand chance it's the playground sand but I'd expect that to be inert.
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post #3 of 4 (permalink) Old 09-05-2020, 04:52 PM Thread Starter
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Yup, that's what I suspected. I'll take them out no matter what in the meantime, and test them like you've suggested. Thanks!
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post #4 of 4 (permalink) Old 09-07-2020, 04:57 PM Thread Starter
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Damn it! The so-called "pea gravel" must be a culprit too, as the TDS reads 270 ppm. I'm pulling everything out and replacing it with HTH pool filter sand. Ugh.
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