In my fish tank the KH has dropped from 180ppm to 40ppm!

[Rocksie]

My tap water comes from a well and has no chlorine. It is VERY hard. GH tests at 300ppm. KH tests at 180ppm out of the tap. But the KH in the tank has dropped to a reading of 40ppm!!

My tank is only 20 gallons. I know a larger tank is better but that is what I have (long story). There are no snails yet, but I'm about to do a new aquascape and add lots of plants that have snails on them so I hope between the snails and the increased number of plants, the water parameters will improve.

The tank houses a pair of Sunset Platys and their 3 fry (in a net box), an orphaned ~3.5 month old male Black Lyre-Tailed Molly, 4 Danio Glo Fish, and a female Red Mickey Mouse Platy.

I have a Marineland Penguin 150 filter with a regular carbon filter and a nitrate filter.

Can someone tell me what is causing the KH to drop and how I can fix it and prevent it from dropping in the future?

 

[StevenF]

I saw this in the past when I was trying to get my phosphate levels under control. I eventually determined that the high phosphate levels in my tank were due to insufficient nitrogen in the water for my plants. So I started to add some nitrogen fertilizer and that helped dropped the phosphate levels. The resulting improved plant growth allowed the plants to consume the phosphates and other elements that my have been high. The drop was rapid and got about as low as you are reporting. No harm was done to my fish.

I have since read that phosphate is known to affect PH and alkalinity although I don't understand why that is. If you have no plants in the tank yet it might indicate algae has drifted through the air into the tanks and is growing and consuming some excess nutrients. But that is just a guess. I think adding the plants will do more to stabilize the tank. At this time i would not recommend doing anything other than maybe a water change. But I don't think a water change will help

Note for the last 2 years my alkalinity has been at around 40 to about 60 and my PH is generally close to 7. i have shrimp in the aquarium and a KH of 40 doesn't appear to be having any harmful effects. Also I don't believe an alkalinity of 180 is harmful although I have never had it that high.

 

[Rocksie]

I don't seem to have an algae problem in the fish tank though in the plant-nursery tank there is more -- which seems counter-intuitive given the ever-burgeoning snail population. I am relieved that neither my tap water's KH of 180, nor the mysterious drop in the fish tank to a KH of 40 ought to be a problem. I will add more plants (and the accompanying snails), soon and I hope that will make the water parameters much more comfortable and beneficial to my beautiful little fish. I do love them and want them to be healthy. They are so lovely!

 

[mark4785]

Algae and higher plants are able to utilize carbonate hardness content for growth I believe. So to stop them from doing this at an inappropriate rate you should consider adding c02 injection or lowering your aquarium light level. Doing either or both of these things will slow down the rate at which the plants deplete the KH level.

Ensuring the KH level alters slowly also ensures that you do not suffer any deadly pH crashes since, as you probably know, the KH is a pH buffer.

 

[Byron]

Algae and higher plants are able to utilize carbonate hardness content for growth I believe. So to stop them from doing this at an inappropriate rate you should consider adding c02 injection or lowering your aquarium light level. Doing either or both of these things will slow down the rate at which the plants deplete the KH level.

Ensuring the KH level alters slowly also ensures that you do not suffer any deadly pH crashes since, as you probably know, the KH is a pH buffer.

Some plants can use bicarbonates, some may but rarely do, and some cannot. Hard water species such as Vallisneria sp. are efficient at using bicarbonates, but soft water species less so. Ceratopteris, Echinodorus sp, Ludwigia, Nuphar, and all mosses are a few that do not use bicarbonates. There will usually be sufficient CO2 occurring from natural processes primarily in the substrate to satisfy most plants' needs. Of course, the GH/KH/pH, plant species and number, light intensity, fish load/feeding, and the availability of the other nutrients all factor in to this. But chances are that unless tha tank is fairly hard water, and plants native to such water are present, plant uptake of bicarbonates will be very minimal, and certainly not to the extent mentioned in post #1.

Adding diffused CO2 is not likely to help, from what I have read. CO2 produces carbonic acid and this readily binds with any minerals and carbonates. The effect would be to reduce even further the bicarbonates (and general hardness). So if the OP adds CO2, we would expect to see the KH lower further, not rise. At least that is how I understand it (always open to correction).

Byron.

 

[mark4785]

Some plants can use bicarbonates, some may but rarely do, and some cannot. Hard water species such as Vallisneria sp. are efficient at using bicarbonates, but soft water species less so. Ceratopteris, Echinodorus sp, Ludwigia, Nuphar, and all mosses are a few that do not use bicarbonates. There will usually be sufficient CO2 occurring from natural processes primarily in the substrate to satisfy most plants' needs. Of course, the GH/KH/pH, plant species and number, light intensity, fish load/feeding, and the availability of the other nutrients all factor in to this. But chances are that unless tha tank is fairly hard water, and plants native to such water are present, plant uptake of bicarbonates will be very minimal, and certainly not to the extent mentioned in post #1.

Adding diffused CO2 is not likely to help, from what I have read. CO2 produces carbonic acid and this readily binds with any minerals and carbonates. The effect would be to reduce even further the bicarbonates (and general hardness). So if the OP adds CO2, we would expect to see the KH lower further, not rise. At least that is how I understand it (always open to correction).

Byron.

If such hard water species are present in abundance I would apply my original advice and switch to c02 injection so they uptake more carbonic acid as opposed to the bicarbonates from the KH. As for carbonic acid having a reducing effect on KH, I'm not so sure about that. From experience, a KH value will reduce through dillution and metabolic processes associated with the fish and plants absorbing the micro-nutrient content of KH (such as magnesium and iron) which is exacerbated by variables such a higher water temperature. Plants will take up copious amounts of both carbonates and micro-nutrients but will only take up the latter if a sufficient rate of c02 injection is made available to the plant.

In summary my advice is to do any one of the following to reduce the KH reduction rate

• introduce co2 injection so your plants uptake this rather than the carbonates (KH).
• reduce the water temperature to slow down the rate of KH uptake
• Slow down KH dilution by doing frequent water changes with KH-rich water.
• You could try removing some plants if your aquarium is very heavily planted to reduce magnesium/iron uptake which are constituents of KH.

A quote taken from http://advocate.gaalliance.org/calcium-and-magnesium-use-in-aquaculture/#sthash.waSCJ4PG.dpuf on aquatic plant photosynthesis processes

"After plants deplete the water of free carbon dioxide, they can use bicarbonate as a carbon source. But when using bicarbonate, plants release carbonate that hydrolyses and causes pH to increase. Calcium ions react at elevated pH to precipitate carbonate ions as calcium carbonate, and this reaction minimizes the amount of carbonate in the water to hydrolyze and increase pH."

In short, plants will prefer free carbon dioxide, where dosed sufficiently, over bicarbonates of KH so the addition of injected co2 would be beneficial to slowing down the rate of KH depletion.

 

[Byron]

I cannot see that reasoning holding here, sorry. First, there are not that many plants in the aquarium (if memory serves me from another thread by the OP), she is planning to add some. Second, the pH is not rising, and carbonates are not precipitating.

 

[StevenF]

• introduce co2 injection so your plants uptake this rather than the carbonates (KH).

If you take pure water with CO2 dissolved in it and measure the KH you will get a KH reading of zero. If you also measure the PH you will see it is an acid. I have seen this every time I test my RO water. The KH test does not detect the CO2, HCO3, or CO3. Adding CO2 will not elevate KH.

KH overall is mainly a measurement of the ratio of carbonate acid to bases in the aquarium. Common bases in an aquarium are sodium, potassium, calcium, and magnesium. These elements will increase PH. Hydrogen is an acid and will lower PH. Plants can absorb CO2 directly through the leaves or by adsorbing a carbonate throughs the roots.

When the plants absorb a carbonate throughs the root they break it down. So if the plant takes in potassium carbonate the plant will use the potassium and use the CO2 attached to it. The removed CO2 is rapidly replace by CO2 from the air. The Potassium loss however can only be replaced by fertilizing or by adding food or a water change. The end result of this is PH will drop and KH will drop. However in most aquariums there is very little potassium carbonate. Instead you will mostly find potassium chloride, potassium sulfate, and potassium nitrate. Most plants don't use sodium so it generally will not effect KH even though it can be a carbonate..

Calcium and magnesium carbonate are common in aquariums. They are the mainly the carbonates used by plants. IF a plant takes up these, KH can drop due to the loss of calcium and magnessium. Not the loss of CO2. However calcium and magnesium are trace nutrients for plants. So Plants generally don't need a lot of calcium or magnesium .
The real issues for the KH drop reported is that phosphate will interfere with The KH test. However for that to be the case you would need a lot of phosphate to have the effect. Since phosphate is a macro nutrient some aquariums will have a lot of it in the water. High phosphate levels are frequently an indication of low plant growth caused by a nutrient deficiency. That is what happened to me.

However in the case of Rocksie plants were just added to hard water that likely has a lot of nutrients in it. and some carbonates. The new plants used the nutrients and as a result depleted the carbonates. Plant growth was probably very fast for a short time until some of the excess nutrients were depleted. Regular water changes and stable plant growth should stabilize KH. Good aeration should also stabilize CO2.

The high GH reading indicates the water should have plenty of magnesium and calcium. However most of it is probably not in the form of Carbonates. A small fraction is carbonates. For some reason the plants in her aquarium favored the carbonates over the other forms of calcium and magnesium.