Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
TDS meters measure the electrical conductivity of the water. Almost all of this is from ions, that is, charged particles in the water.
This can be almost everything: Salts (not just sodium chloride), minerals, organic materials... so TDS is a reasonable way to measure all the 'stuff' in the water.
You simply do not have all the tests you need to figure out what is raising the TDS.
You may not need more tests. Just go with it. When the GH is right for the livestock, and the KH stabilizes the pH in the right range, then the minerals are probably right for the livestock.
As suggested above: The plants are probably removing most of the nitrogen in all its forms, so the tank is cycled in this sense, and is ready for stocking.
Here is something you can try:
Test each of these separately.
1) Tap water, no additives.
2a,b,c...) Tap water with just ONE additive: Dechlor, shrimp minerals, each of the plant fertilizers...
3) Make up some new water for a water change with all the additives in the right ratio.
If number 3 does not match the tank then there is something in the tank contributing to the water chemistry.
4a,b,c...) Take each item out of the tank and test it separately in a jar of water. Rock, driftwood, a handful of substrate... A slow reacting item might take a week or two to show up.
Here is an example of TDS not matching (limited) tests:
I buy fish from several stores.
I set up quarantine tanks to match the water the fish are in at the store.
When I buy new fish I test the water in the bag.
One store had the following values:
GH and KH around 10-12 degrees. (About double or more of my tap water)
TDS in the low thousands. Not kidding. TDS around 1100-1200ppm.
So I got out my API Pond Salt Test. YUP! The store is salting their water for FRESH water fish. A lot!
I could have quarantined my new fish in my BRACKISH water tank! (It is a very low end brackish tank, but still....!)
So I set up the Q-tank with GH and KH about 12 degrees and started adding salt (sodium chloride) until the TDS matched the bag.
It took a month of small water changes to get the fish acclimated to the water in my display tanks.
Side issue: Why sell specialized minerals for shrimp tanks? How do they know what minerals you need to supplement what might already be in the water? Or are they assuming you are starting with pure RO, no other minerals added?