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Water quality

Maintaining a healthy system for fish, bacteria and plants, is all about keeping things in balance. It is sometimes a compromise between what is ideal for the different living organisms. This is why monitoring water quality is always important, but particularly so in the early weeks, while the system is establishing itself. It is a good idea to record all results, and any adjustments and additions made to the water, both for your own reference and to make it easier for us to help if you require support.

Sample tables are available 'here'. There are a number of different factors relating to water quality we must be aware of, how to monitor them and what to do are explained below.

Dissolved Oxygen
Fish use oxygen for respiration, therefore having dissolved oxygen above 5mg/litre is vital in a FishPlant system.

Testing for dissolved oxygen is difficult and expensive, however, by ensuring all the other water quality factors are ok and there is sufficient water movement and aeration (and the water temperature is not too high) we can be confident there is enough dissolved oxygen in the water.

The return valve on the Flow Fitting will constantly move water around your tank, and the AutoSiphon draining into your FishTank both help increase dissolved oxygen. Water will hold less dissolved oxygen when it is warmer, so if you are heating the FishTank above 16°C (e.g. for Tilapia) we strongly recommend additional aeration – a FishPlant Air-pump and FishPlant Air-stone – thought you may wish to add them even for cold water.

Acidity or ‘pH’
Acidity is measured as ‘pH’ and is a scale of 1-14, with 7 being neutral, 1 being most acidic and 14 being most alkaline.

In your FishPlant Family Unit you MUST keep the pH between 6 and 8. Once the system is running successfully, the pH is likely to FALL and should be monitored and adjusted regularly.

The FishPlant ‘Fish Care’ water quality test kit contains a pH test, and also an Alkalinity (or KH) test that helps monitor how stable the pH is. As, once your system is running effectively, the pH test is the one most used, there is also a separate FishPlant ‘pH Test kit’.

The pH should be adjusted up using FishPlant pH Up, this is food grade Potassium Hydroxide in a relatively weak dilution for safe use, but should still be kept out of the reach of children. The potassium in it is available to the plants to use.

Dilute further with either topping up water or water from the FishTank and pour back through the PlantBed.

Water ‘Hardness’
Our water supply is normally described as either ‘soft’ or ‘hard’. This depends on how much dissolved solids (mainly Calcium and Magnesium Carbonates) there is in it.

Hardness is often expressed as ‘mg/litre CaCO3’:

• Soft water 0-75 mg/litre CaCO3
• Moderately hard water 75-150 mg/litre CaCO3
• Hard water 150-300 mg/litre CaCO3
• Very hard water >300 mg/litre CaCO3

How ‘hard’ your water is, affects many other parameters within your FishTank, especially the ‘pH’ and how likely it is to fluctuate. Very ‘soft’ water may not contain enough Calcium for plants to grow well, and very ‘hard’ water can lead to too much Calcium building up in the water, than is good for the fish.

The FishPlant ‘Plant Care’ water quality test kit contains a ‘General Hardness (GH)’ test, that is measured in °DH. If the water from your supply is less than 3°DH, it may be necessary to add Calcium in the form of either Hydroxide or Carbonate, for the plants and to help stabilise pH.

If the GH in the FishTank builds up over time to 30°DH you should start doing partial water changes (not more than 10% at a time) to keep it below this level.

Very Hard Water - already has large amounts of dissolved solids in it and if it is suitable at all for fish, will very quickly reach GH levels that require regular partial water changes thus wasting much of the produced plant nutrients. It is also likely to have a high pH and may require adjusting down before use.

There are chemical water softeners available but the water would not be suitable for keeping fish. There are water filters available that will reduce the hardness of the mains supply, or even produce deionised water but they are expensive – if you use ‘Reverse Osmosis’ filter remember to mix that back with some unfiltered water or it will be too soft.

The other option is to mix the hard water with some collected rain water, but it must be ensured the collected water is clean and preferably filtered for solids before use. Rain water is often slightly acidic so will help reduce the pH of the hard water.

Very soft water – may require supplementary Calcium for the plants to grow well. Calcium Hydroxide can be added in small quantities to a new system and to topping up water, and being alkaline will help with pH control. It is caustic however so care must be taken with it’s use.

A layer of shells can be placed halfway up the PlantBed amongst the clay pebbles, they will gradually dissolve releasing Calcium into the water. They will eventually disappear altogether though and it may be better to place a muslin bag of broken shells in the FishTank, and replace this occasionally as a more easily replenishable source. Make sure the shells are washed thoroughly first.

Soft Water will also be more prone to pH fluctuation and will require more frequent testing and adjustment, particularly in a new system.

The Nitrification process
The waste that fish produce contains Ammonia, which Nitrosomonas bacteria convert to Nitrite, which in turn Nitrobacter bacteria convert to Nitrate.

Ammonia and Nitrite are toxic to fish when they reach high levels, whereas Nitrate is the form of ‘Nitrogen’, plants need most. So we can see how important it is that the Nitrification process works smoothly – this is why we must only stock the FishTank slowly, allowing the numbers of bacteria to increase to cope. Nitrates are safe for fish except at very high levels, so we should not run a system for a long time with no plants, unless we do partial water changes.

The FishPlant ‘Fish Care’ water quality test kit contains both ammonia and nitrite tests and shows the real danger levels, but we should be aiming for these to both be zero. More fish should NOT be added to a FishTank when either of these is above zero. If either the ammonia or nitrite measurements show dangerous levels for fish, partial water changes should be carried out (NEVER more than 20%).