Problems with marine water

Troubleshooting for marine aquariums

There is a solution to almost every problem! And the hardest part is finding the cause of the problem. But for that there are good water tests, helpful pet shop staff and also good marine water forums on the internet. An outline of the most frequently arising problems and their corresponding solutions can be found here:

Problems with the water values

Some marine aquarium owners have trouble raising the pH level of their water above 8.0. With a carbonate hardness between 7 and 10 the pH value ought to stay above 8.0. Reasons for too low pH values could be:

The chalk reactor has been set incorrectly, so that CO2 reached the aquarium water or too much acidic water flows back from the chalk reactor into your aquarium. See Installation technical items .

Each biologically active filter produces acids which then decrease the pH value. Just place a layer of calcareous material as your last filter media into the bio-filter where it will bind the acid.

You can find a summary of all water values for marine aquariums and suggestions for optimising them here: Water values .

Algae problems

The question is whether your „ornamental algae“ aren’t growing as desired or whether you have too many unwanted algae!

Quite a few of higher developed algae (Halimeda, Caulerpa) just grow in good conditions, although they grow in the wild even in “bad” environmental conditions (e.g. in harbours).

If your desired algae don’t grow, please check whether there are „dead zones“ in your aquarium. These are areas on the ground or inside the decoration where the waste accumulates. You can avoid such dead zones with the help of flow pumps or by siphoning. Soiled filter material also reduces the water quality (redox potential) and counteracts a growth of beautiful algae. Often the algae grow immediately when the dirt areas have disappeared.

Red coralline algae mostly grow badly or not at all when the magnesium level lies below 1000 mg/l. You can quickly and easily raise the magnesium value by adding JBL MagnesiuMarin you can quickly and easily raise the magnesium value.

In case you have too much of your chosen algae please DON’T remove too many algae in one go; do it gradually over several days!

Unwanted algae: Chaetomorpha (spaghetti algae), Cladophoropsis, thread algae, diatoms (brown algae), bubble algae (Valonia & Ventricaria) and smear algae are the most common algae pests.

Generally speaking, algae also grow in the wild where an excess of nutrients is available. Please monitor the nitrate and phosphate values and take countermeasures, if required.

You can find more information under Water values and Marine water - the water .

It so happens that the symbiotic algae (Zooxanthellae) also require nitrates and phosphates in their corals’ tissue to survive. As soon as you reduce the nitrate and phosphate values towards zero your corals’ growth rate decreases. This means you need to find a compromise between reducing unwanted algae growth and maintaining the health of the corals.

Support algae reduction by mechanical removal and the use of predators. Wavy turbans, sea urchins and surgeonfish, for example, are all good algae eaters. At all costs prevent the algae from overgrowing your invertebrates! Diatoms are easily to combat. They form when your starting water contains too many silicates (silicic acid; SiO2). With the help of a good silicate remover ( JBL SilicatEx Rapid ) you can remove silicic acid from your water to deprive them of their means of growth.

Example: an aquarium has not yet been equipped with flow pumps. An ORP measurement indicates a value of 200 mV. Now a flow pump is used which generates a water movement, whirling up some dead zones behind the decoration to disperse them. The redox value drops in the short term (whirled up sludge) and settles afterwards again on a higher level than before (dead zone no longer exists). An improvement of water quality has taken place (less reducing processes in the water). When using more flow pumps, their best positions can be ascertained by means of the ORP measurement. The same applies for the best filter positioning and ground siltation, as they all have an influence on the redox value without being directly measurable by commercially available tests. If you raise your redox value by approx. 150 -200 mV the smear algae will very likely disappear. Here the motto is: try out changes in your aquarium individually, evaluate the result with the redox value and continue to make changes until you have achieved the desired result!


Bristle worms, parasites, glass anemones and other unwanted aquarium dwellers sometimes cause problems which need to be solved. The more accurately you identify the problematic dweller the better it can be combatted!

Bristle worms

Although they live hidden and are active at night you can sometimes observe these bristly predators in your aquarium. Because of their predatory habits and because of their enormous size (they can become 200 cm long!) they are dangerous for your aquarium dwellers.

You can remove bristle worms with pincers ( JBL PROSCAPE TOOLS P STRAIGHT ).

If you add a food tablet ( JBL NovoTab ) during the dark phase in your aquarium, not the fish but the worms will emerge to eat it. That way you can see whether there are many worms present and remove some of them. There are also bristle worm traps which do a good job.

You combat them best with predators. Both wrasse species Macropharyngodon bipartitus and

Halichoeres chrysus are great bristle worm eaters which leave other invertebrates alone.

The beautiful comets (Calloplesiops altivelis) are also said to be good bristle worm eaters.

Some snail species are used for pest control: miter and Babylonia species.

The shrimp Stenopus hispidus looks for bristle worms at night. Emptying out the aquarium helps only to a limited degree since the bristle worms withdraw into the holes and crevices of the living rock.

Glass anemones

One glass anemone is quite nice but it immediately becomes hundred! Therefore please react as soon as possible, whenever you discover a glass anemone.

Glass anemones decline with very low phosphate (<0.1 mg/l) and nitrate values (< 3 mg/l). Feeding them with plankton promotes the glass anemones’ reproduction and growth greatly. It is difficult, if not impossible to remove glass anemones by hand. Quite a few aquarium owners have reported success in combatting them by injecting 30 % hydrochloric acid (0.25 ml/glass anemone). But adding hydrochloric acid will make the pH level of your aquarium water drop, so don’t inject too much acid in one go!

Predators of the glass anemones: butterflyfish species Chaetodon kleini, beaked coral fish Chelmon rostratus, shrimp Lysmata wurdemanni.

In addition we recommend you insert one pack of activated coal ( JBL Carbomec ultra ) in the filter system to absorb the messenger substances of the glass anemones.

Planaria (flatworms & Turbellaria)

Like slugs platworms can look very pretty, but they also can become a problem for corals when they take the upper hand and infest the corals. You can siphon flatworms off to reduce their stock.

Very suitable is a planaria trap ( JBL PlaCollect ), which catch planaria in a small tube. We strongly advise against the use of chemical means to combat them because of the side effects. Turbellaria can be so well camouflaged that they are hard to find even at second glance. These include, inter alia, the Acropora-eating flatworm Amakusaplana acroporae which can infest Acropora hard corals, causing serious damage. By bathing the affected corals in an iodine bath outside the aquarium (2 ml Betaisodona/l) the Turbellaria become unable to move and can be rinsed off with a strong water jet. The wrasse Pseudocheilinus hexataenia is another recommended predator, which also finds and eats the clutch of worm eggs. Hingebeak shrimp (Rhynchocinetes) can also be good helpers.

Fish refuse the food

Of course the nutrition in the aquarium is not 1:1 equal to the food spectrum in natural habitats. Nevertheless high-quality food is very closely modelled on the food in nature in its composition. Although granulates or flakes have another shape than the usual food and they don’t move! That’s why fish sometimes need some time to get used to it and to accept it. Other fish are often a big help because they show how to eat the food. Food envy then achieves what was impossible before.

A good way to accustom fish to “new food” is, to select a food which the fish already know from their habitat. JBL PlanktonPur MEDIUM is such a food because it consists of 100 % natural plankton. If the fish have accepted this food the step to flake or granulate is no longer so difficult.

At worst the feed refusal could be caused by illness. The reason could be intestinal parasites. But this case is extremely rare.

Corals become white (coral bleaching)

This process is triggered by water temperatures above 30 °C. The corals reject the symbiotic algae (Zooxanthellae), which live in their tissue, and in doing this lose their colour. You therefore need to take care that your water temperature doesn’t rise above 29 °C. With the help of small fans which generate cooling by evaporation on the water surface, you can avoid this. Another solution is cooling units which however cost a lot of money. It can happen that the corals regain their colour. But the chance is small. Most corals die off after the bleaching.

Fish disappear without a trace

The most common cause is that they jump out of the aquarium. Cover panes help to prevent the involuntary suicide. Fish can, of course, die of old age, but mostly predators in the aquarium are the reason. It’s rarely the other fish in the aquarium you deliberately chose and inserted. It is more likely that you have introduced some “invisible” predators along with the life rock. Typical introduced predators are crustaceans and predatory bristle worms.

Neither is easy to remove. It helps when you get up at night to look for them with a red light (torch with red foil). With long and strong pincers ( JBL PROSCAPE TOOLS P STRAIGHT ) or long tongs ( JBL CombiFix ) you can possibly catch these pests. Or you can just set up a trap: a high jar with a food tablet on the bottom ( JBL NovoTab ) and leaned against the stones can lead to success.

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