Q. I have two blue gouramis, two gold gouramis, and three cory catfish in a 10-gallon planted aquarium. Also in the aquarium are four aquatic plant specimens. The plants are jungle and corkscrew Vallisneria. The aquatic plants have slowly shrunk in height over the past two weeks (I have only had this setup for about two and a half weeks). The gravel size is one-eighth inch diameter and is brown, and it is about 11/2 inches from the bottom of the aquarium. Ammonia and nitrite levels are low, and the pH is 6.6. The filter has become clogged with plant debris.
How can I stop the plants from becoming short? Are the gouramis and cories eating them? If so, how can I stop this? Is there anything that I should add to help the aquatic plants grow? Does the pH need to be adjusted?
A. There is nothing wrong with your pH as far as the aquatic plants are concerned. However, there are a few points are worth mentioning. Unless you are adding carbon dioxide to the water (adding carbon dioxide tends to lower the pH), your pH indicates that there is very little carbonate in the water. Vals are one of the few aquatic plants that can get carbon from carbonates besides getting it from carbon dioxide. If everything else is in good order, your plants might benefit from higher carbonate content in the water. You might try adding some calcium carbonate or baking soda (sodium bicarbonate). You can get calcium carbonate from some nurseries, from web vendors that deal in hydroponic gardening and from brew-your-own-wine/beer web stores. About three-fourths of a teaspoon baking soda per 10 gallons of water will increase the carbonate hardness (KH) by 4 degrees and will not increase general hardness (GH). About 11/2 teaspoons of calcium carbonate per 10 gallons of water will increase both the KH and the GH by 4 degrees. If you want to get fancy, you can use some of each in proportion to adjust the KH and GH to desired values. I would add about three-fourths to 1 teaspoon of baking soda or 11/2 to 2 teaspoons of calcium carbonate in your case to get the KH up to roughly 4 or 5. If you do 50-percent water changes each week – always a good idea – add back half those amounts with the new water, adjusting as needed to maintain roughly 4 or 5 degrees KH. You can get a KH test kit from the local fish store. They are inexpensive and easy to use.
However, from what you have written, I do not think increased carbonates alone will solve your problem. My guess is that your aquatic plants are undernourished. This always leads to stunted growth and eventually a premature end. As the live aquatic plant mass dies back, the detritus ends up on the substrate and in the filter. Look through my previous columns on the FishChannel.com website; you should find enough information to restore your aquatic plants. In particular, take a look at the sections about nutrients:
Different aquatic plants have different needs
Healthy plants require balanced growing conditions