22 



H. J. THOMAS 





Figure 1. — Circulation system of the main aquarium: B, experimental benches (high and low) ; 

 C, cooling coils ; Di to Dg, large display tanks ; rfi to ds, small display tanks ; E, immersion heater; 

 F, filter ; H, header tank ; Pi, main circulation pump ; P2, cooling circulation pump ; R, reservoir- 

 sedimentation tank (duplicated) ; 8, service tank. 



Valves are of the rubber diaphragm 

 type with vulcanite linings (Dexine Rub- 

 ber & Ebonite Ltd. ) . 



Cut-in/cut-out electrical probes have 

 carbon contacts (stainless-steel probes 

 were found to be unsatisfactory) con- 

 nected to relays (Sunvic Controls Ltd.). 



Air at 10 to 14 pounds' pressure is sup- 

 plied by a water-sealed compressor (Nash 

 Engineering Company). This avoids oil 

 droplets in the air compressed by oil- 

 sealed pumps. A trap fitted with a float 

 valve collects and drains off the fresh wa- 

 ter arising from droplets carried over 

 with the compressed air. Aeration facili- 

 ties are provided to each tank, but their 

 use is exceptional where tanks are on cir- 

 culation. 



OPERATING DATA 



The twin reservoir-sedimentation tanks, 

 each of 40,000 gallons' capacity, are used 

 in the circulation on alternate weeks. 



Sea water is added to the system to 

 make up for losses in siphoning and main- 

 tenance ; to provide the maximum refresh- 

 ing, any surplus water is run off so that 

 an addition of clean sea water can be made 

 at the rate of 4,000 gallons monthly. In- 

 coming water is added to the tank not on 

 circulation, thereby allowing a period for 

 seasoning. Sea water is transported by 

 lorry in a collapsible Portolite container 

 (Marston Excelsior Ltd., I.C.L). 



The sand filter bed comprising twin sec- 

 tions is wholly in use except for the shut- 

 ting off of a half section for periodic 

 maintenance. This procedure maintains 

 the filters in a much better condition than 

 alternate use. The pattern of the filter is 

 that normal for domestic fresh-water sup- 

 plies, but incorporated in the bottom of the 

 filter is a layer of coarse marble chips. 

 This is considered to be responsible for 

 the marked stability of the pH in the 

 aquariimi, which has constantly remained 



