Beat the heat

At this time of year you can spend long, warm even­ings en­joy­ing your pond fish, which are at their most ac­tive right now. But ris­ing tem­per­a­tures can cause prob­lems. Here’s how to pre­vent them.

Practical Fishkeeping (UK) - - Welcome - WORDS: DAVE HULSE, TECH­NI­CAL CON­SUL­TANT AT TE­TRA

Sum­mer tem­per­a­tures can cause prob­lems for pond fish. Here’s how to pre­vent them.

After bring­ing your pond through the del­i­cate spring pe­riod, sum­mer is the time to lie back and ap­pre­ci­ate your hard work. How­ever, there are sev­eral unique prob­lems that can arise in pond wa­ter at this time of year.

Warm wa­ter wor­ries

One of the prop­er­ties of wa­ter is that as it cools down it can hold more dis­solved oxy­gen. A sam­ple of fresh­wa­ter at 5°C is sat­u­rated with oxy­gen at 12.76 mg/l. How­ever, a sam­ple of wa­ter at 25°C is sat­u­rated when it holds only 8.24 mg/l of oxy­gen.

So, what are the im­pli­ca­tions of this for our pond? Firstly, there is less oxy­gen avail­able to the fish when the wa­ter is warmer, but to ex­ac­er­bate the sit­u­a­tion the fish be­come more ac­tive at higher tem­per­a­tures, mean­ing they have a greater de­mand for oxy­gen. For ev­ery 10°C rise in tem­per­a­ture the meta­bolic rate of the fish roughly dou­bles.

It is not only the fish that will have a greater oxy­gen de­mand, the ac­tiv­ity of the fil­ter bac­te­ria is also dic­tated by tem­per­a­ture — the warmer the wa­ter the faster they metabolise. Cou­ple this with a greater pro­duc­tion of am­mo­nia by the fish, and the in­creased over­all con­sump­tion of oxy­gen by liv­ing or­gan­isms in the pond, the amount of oxy­gen avail­able is at an an­nual low.

To man­age this sum­mer oxy­gen para­dox, it is es­sen­tial to en­sure that the wa­ter is thor­oughly oxy­genated through­out the sum­mer. The best way to do this is to use a test kit to an­a­lyse the oxy­gen level to en­sure it re­mains at a value that can meet the re­quire­ments of fish and fil­ter bac­te­ria.

Oxy­gen con­cen­tra­tion can be ex­pressed in mg/l (or the sim­i­lar ex­pres­sion; ppm), but this fails to ac­count for the sat­u­ra­tion value of oxy­gen in the wa­ter. A more con­ve­nient ex­pres­sion is per­cent­age sat­u­ra­tion. For ex­am­ple, fresh­wa­ter at 25°C holds 8.24 mg/l of oxy­gen at 100% sat­u­ra­tion, if the level dropped to 6 mg/l then the sam­ple would be 72.8 % sat­u­ra­tion.

As such, dur­ing the sum­mer months you need to be es­pe­cially vig­i­lant of dis­solved oxy­gen lev­els in the pond. Reg­u­lar test­ing is use­ful, thor­ough aer­a­tion of the wa­ter by air­stones, ven­turis, wa­ter­falls and/or foun­tains is es­sen­tial. Dur­ing es­pe­cially hot and hu­mid days, the dis­solved oxy­gen level can be at its low­est — al­ways make sure you have hit a min­i­mum of 60% sat­u­ra­tion but strive for a value nearer to 80%. The closer biofil­tra­tion cham­bers are to sat­u­ra­tion with dis­solved oxy­gen the bet­ter they func­tion.

The dan­gers of al­gae blooms

An­other prob­lem that can arise in ponds in the sum­mer is blooms in the growth of un­sightly blan­ketweed and green wa­ter al­gae. These prim­i­tive plants have ba­sic re­quire­ments in­clud­ing dis­solved nu­tri­ents such as ni­trate and phos­phate and sun­light to al­low them to pho­to­syn­the­sise. In many ponds al­gae be­comes a real prob­lem in the sum­mer as the sun­light reaches the cor­rect in­ten­sity and shines for a suf­fi­ciently long pe­riod of time to al­low al­gal growth to pro­ceed at a max­i­mal rate. Te­tra Pond Al­go­fin and Al­go­rem can help to safely and ef­fec­tively treat al­gae prob­lems. Apart from look­ing un­sightly, al­gae can cause nu­mer­ous wa­ter qual­ity based prob­lems. On a ba­sic level, al­gal cells and strands of blan­ketweed soon clog fil­tra­tion sys­tems, mean­ing you’ll need to carry out more rou­tine main­te­nance to keep the life sup­port sys­tem of the pond run­ning ef­fi­ciently.

Down at a chem­i­cal level the pond wa­ter is be­ing pro­foundly in­flu­enced by the growth of al­gae. The pho­to­syn­thetic pro­cesses which oc­cur only in day­light hours, sees the lib­er­a­tion of oxy­gen and the up­take of car­bon diox­ide. These pro­cesses oc­cur at the same time as the nor­mal res­pi­ra­tion of the plant, but there is an over­all in­crease in oxy­gen and de­crease in car­bon diox­ide in a pond with heavy growths of plant life.

At night pho­to­syn­the­sis stops, but res­pi­ra­tion con­tin­ues lead­ing to a de­crease in oxy­gen lev­els and in­crease in car­bon diox­ide, a trend that con­tin­ues un­til sun­rise.

How does this af­fect the fish?

Firstly, the oxy­gen level in the pond will be far from sta­ble, lakes heav­ily choked with al­gal growth have been recorded fluc­tu­at­ing from a su­per­sat­u­rated 169% down to a low of 39%. Such in­sta­bil­ity causes chronic stress to fish and would need to be reme­died.

An­other prob­lem is the car­bon diox­ide re­lease which in­creases at night. The chem­istry of car­bon diox­ide in wa­ter is very com­plex, but can gen­er­ally be con­sid­ered to lower the ph as it leads to the for­ma­tion of car­bonic acid, mean­ing that more car­bon diox­ide leads to a lower ph.

The ph is held sta­ble by the buffer­ing sys­tem or car­bon­ate hard­ness (KH) in the wa­ter. Ponds with a good strong KH (>6 °H) can re­sist the change in ph for a de­cent length of time, as the KH can buf­fer the car­bonic acid. Re­mem­ber though that KH can be­come ex­hausted and is best re­placed by a wa­ter change with hard to mod­er­ately hard wa­ter. If you live in a soft wa­ter area of the coun­try then KH can be raised by plac­ing cockle or oys­ter shell into the fi­nal stage of the fil­tra­tion sys­tem. Al­ter­na­tively, you can im­prove wa­ter qual­ity by adding Te­tra Pond Wa­ter Bal­ance which helps to main­tain the cor­rect wa­ter con­di­tions, sta­bil­is­ing ph and KH to pro­mote a health­ier pond en­vi­ron­ment.

So, you can see that a pond choked with al­gae is a po­ten­tially dan­ger­ous en­vi­ron­ment for the pond as well as an eye­sore.

The ac­tion plan in­volves get­ting rid of the al­gae, en­sur­ing the oxy­gen level is not fluc­tu­at­ing by vig­or­ously aer­at­ing the wa­ter, es­pe­cially at night, and fi­nally en­sur­ing the pond is not suf­fer­ing daily fluc­tu­a­tions in ph by main­tain­ing a good level of KH in the pond wa­ter.

Sum­mer is the time to get out and re­lax by your pond — but are your fish as happy to see the warm weather as you are?

Sum­mer blan­ketweed isn’t just un­sightly — it could lead to a wipe out in your pond!

Widely fluc­tu­at­ing oxy­gen lev­els are highly stress­ful for your fish.

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