Seachem is renowned for its water additives. Their line of buffers and pH regulators is second to none.
Acid Buffer - Seachem acid buffer adjusts pH to between 5 and 8. You can use it in conjunction with alkaline buffer to target a pH. Acid buffer contains no phosphates, so it is great to use in planted tanks or in tanks where a phosphate based buffers might cloud the water (such as tanks with very hard water).
Alkaline Buffer - Seachem alkaline buffer adjusts pH to between 7.2 and 8.5. You can use it with acid buffer to target a specific pH. Alkaline buffer raises pH without phosphates, so it is great to use in planted tanks.
Discus Buffer - Seachem Discus buffer is a phosphate based buffer, so if you have a planted tank it might be best to adjust your pH with Acid Buffer. Discus buffer adjusts pH to 5.8 - 6.8. Use Discus buffer with Neutral Regulator to target a specific pH. In addition to lowering pH Discus buffer also softens water.
Malawi Victoria Buffer - Seachem Malawi Victoria buffer raises pH to 7.8 to 8.4 while raising KH. If you want a pH higher than 8.4 you can use their Tanganyika buffer.
Neutral Regulator - Seachem Neutral Regulator adjusts your pH up or down to 7.0. It also removes chlorine, chloramine, and detoxifies ammonia. This product does contain phosphates, so use sparingly or not at all in planted tanks. To lower pH below 7.0 use with Acid regulator or Discus buffer.
Equilibrium - Seachem Equilibrium is designed to establish the ideal mineral content for planted tanks when using RO/DI water. This product does not contain any sodium or chloride which can be detrimental to plants. If you also like to raise KH you can use this product in conjunction with Alkaline Buffer.
Rivers to Reef says: If you can avoid tinkering with your pH then don't bother. We always advise against pH adjustments because it can be so temperamental. A stable pH is 10 times more important than what a book says is the "proper" pH. One of the quickest ways to kill all the inhabitants of your tank is to adjust pH too quickly. Always adjust pH without anything alive in the tank, and if that is not possible, do so in very small increments.
If you are having a hard time at keeping some plants and fish alive sometimes the problem is hard water and not pH. Test your water hardness (if you are not sure) and if it is hard you can dilute your tap water with distilled or reverse osmosis water (50% is usually adequate). You should never use 100% distilled/RO water as it can strip your fish of its minerals. Use a product like Equilibrium to balance your water without tinkering with pH.