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I have a 10 gallon RCS tank, I use pure RO and re-mineralise with salty shrimp GH+ and baking soda.

I usually do 2.5 gallon WC every other week. I maintain a GH of 7 and KH of 2-3. My plants are showing severe Nitrate deficiencies and Potassium deficiencies. Currently Nitrates are 0ppm.

Tank has moss/camboma, cyrpts, wisteria, rrf/ frogbit and is a low light no co2. I added 5ppm of nitrate today after my water change and I checked my ppms before adding the water and the tds are 200ppm. The water in the tank is tds 210 ppm.

How do people keep tds low while also adding ferts/keeping gh up?
 

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Was that Potassium Nitrate (KNO3)?

What's your substrate? Dosing any other ferts?

GH and KH are more important. I'd just make sure KH and GH are in range. I would say pH and temperature are more important than TDS. With RCS/Neos, they are hardy so I wouldn't be worried. Many people even go into the 300's ppm TDS.

As in the name, TDS, is Total Dissolved Solids, organic and inorganic.
So go ahead and add in the needed N and K, just make sure GH and KH are at the appropriate levels and don't mind the TDS too much.

Potassium (Bi)Carbonate is an alternative in place of baking soda (Sodium bicarbonate).
 

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Ehh, it's just an alternative that I mentioned.
I've never used baking soda in a planted tank before so I don't know if the sodium it contains has much negative impact on plant or fish health (after it accumulates). I have a feeling it wouldn't cause much issue.

If there is no issue, then it's perfectly fine to use baking soda to raise KH. Then you have Potassium Nitrate for N and K, instead of using Potassium Bi/carbonate for K and raising KH, then having to source another N source.
 

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I had the same issue a while back and adjusted my Potassium Nitrate up.

What works for me is I fertilize the incoming water during my weekly 10%. In a 5 gal container, I test the incoming RO for near 0 TDS (electronic pen meter) Then I add my light fert mix (Macros + Florish Iron) . testing again I am only about 10 on TDS meter. Then Fluval Shrimp minerals (5,6 or 7ml depending on how much macros I used) to land at or near 120 TDS and about 5GH for the incoming water. The tank water runs between 130 and 160 TDS and still keeps about 5GH steady.

After the 10% water change my nitrates still show <10ppm, but it seems to be enough weekly to keep the plants from yellowing out and yet not impact my CRS colony from breeding lots.


Ah - you said RCS. Even easier. Tom Barr runs heavy ferts in his main tank with his RCS and swears they are unkillable.
I was running my RCS up at 450TDS and >50 ppm Nitrates for a couple years in my main tank and they were happy little buggers, even with full CO2 and medium ferts.
 
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