Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
EBMUD is VERY soft water. Almost RO.
Unless you are trying to keep wild caught Discus or Cardinal Tetras or a few others, I would add GH booster.
Aim to keep the GH at about 3 German degrees of hardness for most soft water fish. 1 German degree of hardness is 17.9 ppm, so the EBMUD is barely 1 degree (as your test shows).
Most plants are OK with about 3 degrees or more of hardness.
Harder is better for hard water fish like many live bearers, and some Rainbows, and many Cichlids. Harder water is just fine for most plants, too.
KH is also very low, and this means the pH can fluctuate quite easily. If you want to raise the carbonates a bit, then add baking soda. 1 teaspoon of baking soda added to 30 gallons of water will raise the KH by 2 German degrees of hardness.
All the other fertilizers are lacking in this water, too, so get:
Fish food supplies N, P and some traces, but usually not enough K or Fe. In a Walstad, low light tank that is OK, or just a little K and Fe supply is helpful.
In higher light tanks you will need to add all of them.
If your tank is lightly stocked you may not be adding enough nitrogen through the fish food, so you may use enough KNO3 to also supply the K required. It does not hurt to add a bit more, though.
The tiny amount of KH2PO4 that you might add, no matter how high the light, will add so little K it pretty much does not count as a source of K.